Practice this lesson yourself on KhanAcademy.org right now:
https://www.khanacademy.org/math/differential-calculus/limits_topic/squeeze_theorem/e/squeeze-theorem?utm_source=YT&utm_medium=Desc&utm_campaign=DifferentialCalculus

Watch the next lesson: https://www.khanacademy.org/math/differential-calculus/limits_topic/squeeze_theorem/v/squeeze-theorem?utm_source=YT&utm_medium=Desc&utm_campaign=DifferentialCalculus

Missed the previous lesson?
https://www.khanacademy.org/math/differential-calculus/limits_topic/squeeze_theorem/v/squeeze-theorem-exercise-example?utm_source=YT&utm_medium=Desc&utm_campaign=DifferentialCalculus

Differential calculus on Khan Academy: Limit introduction, squeeze theorem, and epsilon-delta definition of limits.

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to KhanAcademy’s Differential Calculus channel:
https://www.youtube.com/channe....l/UCNLzjGl1HBdZrHXo4
Subscribe to KhanAcademy: https://www.youtube.com/subscr....iption_center?add_us

Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/ma....th/multivariable-cal

Example of calculating the flux across a surface by using the Divergence Theorem

Watch the next lesson: https://www.khanacademy.org/math/multivariable-calculus/divergence_theorem_topic/divergence_theorem/v/why-we-got-zero-flux-in-divergence-theorem-example-1?utm_source=YT&utm_medium=Desc&utm_campaign=MultivariableCalculus

Missed the previous lesson?
https://www.khanacademy.org/math/multivariable-calculus/divergence_theorem_topic/divergence_theorem/v/3-d-divergence-theorem-intuition?utm_source=YT&utm_medium=Desc&utm_campaign=MultivariableCalculus

Multivariable Calculus on Khan Academy: Think calculus. Then think algebra II and working with two variables in a single equation. Now generalize and combine these two mathematical concepts, and you begin to see some of what Multivariable calculus entails, only now include multi dimensional thinking. Typical concepts or operations may include: limits and continuity, partial differentiation, multiple integration, scalar functions, and fundamental theorem of calculus in multiple dimensions.

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to KhanAcademy’s Multivariable Calculus channel:
https://www.youtube.com/channe....l/UCQQZDc22yCogOyx6D
Subscribe to KhanAcademy: https://www.youtube.com/subscr....iption_center?add_us

Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/ma....th/algebra2/x2ec2f6f

Sal walks through several examples of how to write g(x) implicitly in terms of f(x) when g(x) is a shift or a reflection of f(x). Created by Sal Khan.

Watch the next lesson: https://www.khanacademy.org/math/algebra2/manipulating-functions/stretching-functions/v/compressing-functions-example?utm_source=YT&utm_medium=Desc&utm_campaign=highschoolmath

Missed the previous lesson? https://www.khanacademy.org/math/algebra2/manipulating-functions/shifting-functions/v/graphing-shifted-functions?utm_source=YT&utm_medium=Desc&utm_campaign=highschoolmath

High School Math on Khan Academy: Did you realize that the word "algebra" comes from Arabic (just like "algorithm" and "al jazeera" and "Aladdin")? And what is so great about algebra anyway? This tutorial doesn't explore algebra so much as it introduces the history and ideas that underpin it.

About Khan Academy: Khan Academy is a nonprofit with a mission to provide a free, world-class education for anyone, anywhere. We believe learners of all ages should have unlimited access to free educational content they can master at their own pace. We use intelligent software, deep data analytics and intuitive user interfaces to help students and teachers around the world. Our resources cover preschool through early college education, including math, biology, chemistry, physics, economics, finance, history, grammar and more. We offer free personalized SAT test prep in partnership with the test developer, the College Board. Khan Academy has been translated into dozens of languages, and 100 million people use our platform worldwide every year. For more information, visit www.khanacademy.org, join us on Facebook or follow us on Twitter at @khanacademy. And remember, you can learn anything.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy’s High School Math channel: https://www.youtube.com/channe....l/UCAj83VTec-NC-g0BK
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

If you already know the area under a curve, you can use it to compute an integral.

Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/ap-calculus-ab/ab-accumulation-riemann-sums/ab-def-integral/e/evaluating-a-definite-integral-from-a-graph?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB

Watch the next lesson: https://www.khanacademy.org/math/ap-calculus-ab/ab-accumulation-riemann-sums/ab-riemann-sums/v/simple-riemann-approximation-using-rectangles?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB

Missed the previous lesson? https://www.khanacademy.org/math/ap-calculus-ab/ab-accumulation-riemann-sums/ab-def-integral/v/definite-integrals-intro?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB

AP Calculus AB on Khan Academy: Bill Scott uses Khan Academy to teach AP Calculus at Phillips Academy in Andover, Massachusetts, and heÕs part of the teaching team that helped develop Khan AcademyÕs AP lessons. Phillips Academy was one of the first schools to teach AP nearly 60 years ago.

About Khan Academy: Khan Academy is a nonprofit with a mission to provide a free, world-class education for anyone, anywhere. We believe learners of all ages should have unlimited access to free educational content they can master at their own pace. We use intelligent software, deep data analytics and intuitive user interfaces to help students and teachers around the world. Our resources cover preschool through early college education, including math, biology, chemistry, physics, economics, finance, history, grammar and more. We offer free personalized SAT test prep in partnership with the test developer, the College Board. Khan Academy has been translated into dozens of languages, and 100 million people use our platform worldwide every year. For more information, visit www.khanacademy.org, join us on Facebook or follow us on Twitter at @khanacademy. And remember, you can learn anything.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan AcademyÕs AP Calculus AB channel: https://www.youtube.com/channe....l/UCyoj0ZF4uw8VTFbml
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Sal continues the discussion on e, this time digging deeper into the mathematical definition of e. Created by Sal Khan.

Watch the next lesson:
https://www.khanacademy.org/economics-finance-domain/core-finance/interest-tutorial/cont-comp-int-and-e/v/continuously-compounding-interest-formula-e?utm_source=YT&utm_medium=Desc&utm_campaign=financeandcapitalmarkets

Missed the previous lesson? Watch here: https://www.khanacademy.org/economics-finance-domain/core-finance/interest-tutorial/cont-comp-int-and-e/v/e-through-compound-interest?utm_source=YT&utm_medium=Desc&utm_campaign=financeandcapitalmarkets

Finance and capital markets on Khan Academy: This is an older tutorial (notice the low-res, bad handwriting) about one of the coolest numbers in reality and how it falls out of our innate desire to compound interest continuously.

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy’s Finance and Capital Markets channel: https://www.youtube.com/channe....l/UCQ1Rt02HirUvBK2D2
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Finding the initial condition based on the result of approximating with Euler's method.

Practice this lesson yourself on KhanAcademy.org right now: https://www.khanacademy.org/math/ap-calculus-bc/bc-diff-equations/bc-eulers-method/e/euler-s-method?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusBC

Watch the next lesson: https://www.khanacademy.org/math/ap-calculus-bc/bc-diff-equations/bc-exp-models/v/modeling-population-with-simple-differential-equation?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusBC

Missed the previous lesson? https://www.khanacademy.org/math/ap-calculus-bc/bc-diff-equations/bc-eulers-method/v/eulers-method?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusBC

AP Calculus BC on Khan Academy: Learn AP Calculus BC - everything from AP Calculus AB plus a few extra goodies, such as Taylor series, to prepare you for the AP Test

About Khan Academy: Khan Academy is a nonprofit with a mission to provide a free, world-class education for anyone, anywhere. We believe learners of all ages should have unlimited access to free educational content they can master at their own pace. We use intelligent software, deep data analytics and intuitive user interfaces to help students and teachers around the world. Our resources cover preschool through early college education, including math, biology, chemistry, physics, economics, finance, history, grammar and more. We offer free personalized SAT test prep in partnership with the test developer, the College Board. Khan Academy has been translated into dozens of languages, and 100 million people use our platform worldwide every year. For more information, visit www.khanacademy.org, join us on Facebook or follow us on Twitter at @khanacademy. And remember, you can learn anything.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy's AP Calculus BC channel: https://www.youtube.com/channe....l/UC5A2DBjjUVNz8axD-
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/ma....th/ap-calculus-ab/ab

Manipulating the expression to make u-substitution a little more obvious. Created by Sal Khan.

Watch the next lesson: https://www.khanacademy.org/math/ap-calculus-ab/ab-antiderivatives-ftc/ab-u-substitution/v/u-substitution-defining-u?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB

Missed the previous lesson? https://www.khanacademy.org/math/ap-calculus-ab/ab-antiderivatives-ftc/ab-u-substitution/v/u-substitution?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB

AP Calculus AB on Khan Academy: Bill Scott uses Khan Academy to teach AP Calculus at Phillips Academy in Andover, Massachusetts, and heÕs part of the teaching team that helped develop Khan AcademyÕs AP lessons. Phillips Academy was one of the first schools to teach AP nearly 60 years ago.

About Khan Academy: Khan Academy is a nonprofit with a mission to provide a free, world-class education for anyone, anywhere. We believe learners of all ages should have unlimited access to free educational content they can master at their own pace. We use intelligent software, deep data analytics and intuitive user interfaces to help students and teachers around the world. Our resources cover preschool through early college education, including math, biology, chemistry, physics, economics, finance, history, grammar and more. We offer free personalized SAT test prep in partnership with the test developer, the College Board. Khan Academy has been translated into dozens of languages, and 100 million people use our platform worldwide every year. For more information, visit www.khanacademy.org, join us on Facebook or follow us on Twitter at @khanacademy. And remember, you can learn anything.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan AcademyÕs AP Calculus AB channel: https://www.youtube.com/channe....l/UCyoj0ZF4uw8VTFbml
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Let's step through some details on how one kind of regulation can reduce economic efficiency

Watch the next lesson: https://www.khanacademy.org/economics-finance-domain/microeconomics/consumer-producer-surplus/deadweight-loss-tutorial/v/minimum-wage-and-price-floors?utm_source=YT&utm_medium=Desc&utm_campaign=microeconomics

Missed the previous lesson? https://www.khanacademy.org/economics-finance-domain/microeconomics/consumer-producer-surplus/consumer-producer-surplus-tut/v/producer-surplus?utm_source=YT&utm_medium=Desc&utm_campaign=microeconomics

Microeconomics on Khan Academy: Topics covered in a traditional college level introductory microeconomics course

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy's Microeconomics channel: https://www.youtube.com/channe....l/UC_6zQ54DjQJdLodws
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/ma....th/precalculus/x9e81


Algebra II on Khan Academy: Your studies in algebra 1 have built a solid foundation from which you can explore linear equations, inequalities, and functions. In algebra 2 we build upon that foundation and not only extend our knowledge of algebra 1, but slowly become capable of tackling the BIG questions of the universe. We'll again touch on systems of equations, inequalities, and functions...but we'll also address exponential and logarithmic functions, logarithms, imaginary and complex numbers, conic sections, and matrices. Don't let these big words intimidate you. We're on this journey with you!

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy’s Algebra II channel:
https://www.youtube.com/channe....l/UCsCA3_VozRtgUT7wW
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

What happens when you add zinc to a solution of copper sulfate? Identifying the half reactions to see what got oxidized and reduced.

Watch the next lesson: https://www.khanacademy.org/science/chemistry/oxidation-reduction/batter-galvanic-voltaic-cell/v/galvanic-cell-voltaic-cell?utm_source=YT&utm_medium=Desc&utm_campaign=chemistry

Missed the previous lesson? https://www.khanacademy.org/science/chemistry/oxidation-reduction/redox-oxidation-reduction/v/redox-titration?utm_source=YT&utm_medium=Desc&utm_campaign=chemistry

Chemistry on Khan Academy: Did you know that everything is made out of chemicals? Chemistry is the study of matter: its composition, properties, and reactivity. This material roughly covers a first-year high school or college course, and a good understanding of algebra is helpful.

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy’s Chemistry channel: https://www.youtube.com/channe....l/UCyEot66LrwWFEMONv
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Watch the next lesson: https://www.khanacademy.org/math/algebra2/rational-expressions/rational-function-graphing/v/example-rational-functions-graphs?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII

Missed the previous lesson?
https://www.khanacademy.org/math/algebra2/rational-expressions/solving-rational-equations/v/rational-inequalities-2?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII

Algebra II on Khan Academy: Your studies in algebra 1 have built a solid foundation from which you can explore linear equations, inequalities, and functions. In algebra 2 we build upon that foundation and not only extend our knowledge of algebra 1, but slowly become capable of tackling the BIG questions of the universe. We'll again touch on systems of equations, inequalities, and functions...but we'll also address exponential and logarithmic functions, logarithms, imaginary and complex numbers, conic sections, and matrices. Don't let these big words intimidate you. We're on this journey with you!

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy’s Algebra II channel:
https://www.youtube.com/channe....l/UCsCA3_VozRtgUT7wW
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Practice this lesson yourself on KhanAcademy.org right now:
https://www.khanacademy.org/math/algebra2/functions_and_graphs/one-variable-modeling/e/understanding-linear-and-exponential-models?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII

Watch the next lesson: https://www.khanacademy.org/math/algebra2/functions_and_graphs/one-variable-modeling/v/constructing-an-exponential-equation-example?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII

Missed the previous lesson?
https://www.khanacademy.org/math/algebra2/functions_and_graphs/one-variable-modeling/v/quadratic-inequality-word-problem?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII

Algebra II on Khan Academy: Your studies in algebra 1 have built a solid foundation from which you can explore linear equations, inequalities, and functions. In algebra 2 we build upon that foundation and not only extend our knowledge of algebra 1, but slowly become capable of tackling the BIG questions of the universe. We'll again touch on systems of equations, inequalities, and functions...but we'll also address exponential and logarithmic functions, logarithms, imaginary and complex numbers, conic sections, and matrices. Don't let these big words intimidate you. We're on this journey with you!

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan Academy’s Algebra II channel:
https://www.youtube.com/channe....l/UCsCA3_VozRtgUT7wW
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/ma....th/ap-calculus-ab/ab

A quick reminder of what limits are, to set up for the formal definition of a limit. Created by Sal Khan.

Watch the next lesson: https://www.khanacademy.org/math/ap-calculus-ab/ab-limits-continuity/ab-limits-opt-vids/v/building-the-idea-of-epsilon-delta-definition?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB

Missed the previous lesson? https://www.khanacademy.org/math/ap-calculus-ab/ab-limits-continuity/ab-limit-strategy/v/flow-chart-of-limit-strategies?utm_source=YT&utm_medium=Desc&utm_campaign=APCalculusAB

AP Calculus AB on Khan Academy: Bill Scott uses Khan Academy to teach AP Calculus at Phillips Academy in Andover, Massachusetts, and heÕs part of the teaching team that helped develop Khan AcademyÕs AP lessons. Phillips Academy was one of the first schools to teach AP nearly 60 years ago.

About Khan Academy: Khan Academy is a nonprofit with a mission to provide a free, world-class education for anyone, anywhere. We believe learners of all ages should have unlimited access to free educational content they can master at their own pace. We use intelligent software, deep data analytics and intuitive user interfaces to help students and teachers around the world. Our resources cover preschool through early college education, including math, biology, chemistry, physics, economics, finance, history, grammar and more. We offer free personalized SAT test prep in partnership with the test developer, the College Board. Khan Academy has been translated into dozens of languages, and 100 million people use our platform worldwide every year. For more information, visit www.khanacademy.org, join us on Facebook or follow us on Twitter at @khanacademy. And remember, you can learn anything.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to Khan AcademyÕs AP Calculus AB channel: https://www.youtube.com/channe....l/UCyoj0ZF4uw8VTFbml
Subscribe to Khan Academy: https://www.youtube.com/subscr....iption_center?add_us

Courses on Khan Academy are always 100% free. Start practicing—and saving your progress—now: https://www.khanacademy.org/ma....th/ap-statistics/den

Discussion of how "normal" a distribution might be

Practice this lesson yourself on KhanAcademy.org right now:
https://www.khanacademy.org/math/probability/statistics-inferential/normal_distribution/e/empirical_rule?utm_source=YT&utm_medium=Desc&utm_campaign=ProbabilityandStatistics

Watch the next lesson: https://www.khanacademy.org/math/probability/statistics-inferential/normal_distribution/v/ck12-org-normal-distribution-problems-empirical-rule?utm_source=YT&utm_medium=Desc&utm_campaign=ProbabilityandStatistics

Missed the previous lesson?
https://www.khanacademy.org/math/probability/statistics-inferential/normal_distribution/v/normal-distribution-excel-exercise?utm_source=YT&utm_medium=Desc&utm_campaign=ProbabilityandStatistics

Probability and statistics on Khan Academy: We dare you to go through a day in which you never consider or use probability. Did you check the weather forecast? Busted! Did you decide to go through the drive through lane vs walk in? Busted again! We are constantly creating hypotheses, making predictions, testing, and analyzing. Our lives are full of probabilities! Statistics is related to probability because much of the data we use when determining probable outcomes comes from our understanding of statistics. In these tutorials, we will cover a range of topics, some which include: independent events, dependent probability, combinatorics, hypothesis testing, descriptive statistics, random variables, probability distributions, regression, and inferential statistics. So buckle up and hop on for a wild ride. We bet you're going to be challenged AND love it!

About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content.

For free. For everyone. Forever. #YouCanLearnAnything

Subscribe to KhanAcademy’s Probability and Statistics channel:
https://www.youtube.com/channe....l/UCRXuOXLW3LcQLWvxb
Subscribe to KhanAcademy: https://www.youtube.com/subscr....iption_center?add_us