# Worked example: recognizing function from Taylor series | Series | AP Calculus BC | Khan Academy | Summary and Q&A

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January 4, 2017
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Worked example: recognizing function from Taylor series | Series | AP Calculus BC | Khan Academy

## TL;DR

The video explains how to identify a function as a Taylor series or Maclaurin series by evaluating the function and its derivatives at zero.

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### Q: How can we determine if a function is a Taylor series or Maclaurin series about zero?

To determine if a function is a Taylor or Maclaurin series about zero, we need to ensure that the function and its derivatives at zero satisfy the constraints mentioned in the video. Specifically, the function at zero should be equal to one, the first derivative at zero should be -1, the second derivative at zero should be 1, and so on.

### Q: What is the general form of a Taylor or Maclaurin series about zero?

The general form of a Taylor or Maclaurin series about zero is f(0) + f'(0)x + f''(0)x^2/2! + f'''(0)x^3/3! + ... Here, f(0) represents the value of the function at zero, f'(0) represents the value of the first derivative at zero, f''(0) represents the value of the second derivative at zero, and so on.

### Q: How can we eliminate some of the choices using the given constraints?

By evaluating the given functions at zero, we can eliminate choices that do not satisfy the constraint that f(0) should be equal to one. For example, the sine function evaluated at zero is zero, which does not meet the constraint. Similarly, the natural logarithm of one plus zero is zero, which also does not meet the constraint.

### Q: Why do we evaluate the derivatives at zero to determine the Taylor or Maclaurin series about zero?

Evaluating the derivatives at zero helps us identify the coefficients of each term in the series. By comparing the coefficients in the given series to the coefficients determined by evaluating the derivatives at zero, we can determine if the function is a Taylor or Maclaurin series about zero.

## Summary & Key Takeaways

• The video introduces the concept of Taylor series and Maclaurin series expansion around zero.

• The general form of a Taylor series or Maclaurin series is discussed, which involves evaluating the function and its derivatives at zero.

• By comparing the given series to the general form, the video demonstrates how to identify which function is the Taylor series or Maclaurin series about zero.