What did I do wrong here? (expressing root x as taylor series about a=4)

In summary, the student made a mistake in their attempt at finding the second Taylor polynomial for the function f(x) = √x. They forgot to include the constant term and also made a mistake with the sign in the degree 2 term. After correcting these errors, they were able to find the correct answer.
  • #1
skyturnred
118
0

Homework Statement



Here is the question:

nxh3n.png


I don't quite know what I did wrong. My method is below.

Homework Equations





The Attempt at a Solution



f(x)=√x
f'(x)=[itex]\frac{1}{2(x)^{1/2}}[/itex]
f''(x)=[itex]\frac{-1}{(2)(2)(x^{3/2}}[/itex]

a=4
f(a)=2
f'(a)=1/4
f''(a)=[itex]\frac{-1}{4(4^{3})^{1/2}}[/itex]

so wouldn't the second taylor polynomial be what I put in the answer field above? Thanks.
 
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  • #2
skyturnred said:

Homework Statement



Here is the question:

nxh3n.png


I don't quite know what I did wrong. My method is below.

Homework Equations

The Attempt at a Solution



f(x)=√x
f'(x)=[itex]\frac{1}{2(x)^{1/2}}[/itex]
f''(x)=[itex]\frac{-1}{(2)(2)(x^{3/2}}[/itex]

a=4
f(a)=2
f'(a)=1/4
f''(a)=[itex]\frac{-1}{4(4^{3})^{1/2}}[/itex]

so wouldn't the second Taylor polynomial be what I put in the answer field above? Thanks.
What you have is the degree 2 term (almost). What's the sign?

Include the constant term & the linear term.
 
  • #3
SammyS said:
What you have is the degree 2 term (almost). What's the sign?

Include the constant term & the linear term.

Oh, so if it asks for T[itex]_{2}[/itex] it also wants the T[itex]_{1}[/itex] and the constant term as well?

Also, I see now that I somehow dropped a negative sign. Thanks!

EDIT: I just tried it and it's correct, so I answered my own question. But thanks again!
 

FAQ: What did I do wrong here? (expressing root x as taylor series about a=4)

1. What is a Taylor series?

A Taylor series is a representation of a function as an infinite sum of terms, where each term is a polynomial expression of increasingly higher order. This series can be used to approximate the value of a function at a certain point or to express the function in a simpler form.

2. How do you express a function as a Taylor series?

To express a function as a Taylor series, you need to find the derivatives of the function at a specific point (known as the center of the series) and plug them into the general formula for a Taylor series. The general formula is f(a) + f'(a)(x-a) + f''(a)(x-a)^2/2! + f'''(a)(x-a)^3/3! + ..., where f'(a), f''(a), and f'''(a) represent the first, second, and third derivatives of the function at the point a, respectively.

3. What is the significance of expressing a function as a Taylor series?

Expressing a function as a Taylor series allows us to approximate the value of the function at any point in its domain. This can be useful for functions that are difficult to evaluate directly, as the Taylor series provides a simpler representation of the function. It also allows us to analyze the behavior of the function around a specific point.

4. Why is the center of the Taylor series important?

The center of the Taylor series is important because it determines the point at which the function is being approximated. The closer the center is to the point of interest, the more accurate the approximation will be. If the center is too far from the point of interest, the Taylor series may not accurately represent the function.

5. How do you express the root x as a Taylor series about a=4?

To express the root x as a Taylor series about a=4, you first need to find the derivatives of the function at the point a=4. Then, plug these derivatives into the general formula for a Taylor series to get the series representation of the function. The resulting series will be a polynomial expression of increasingly higher order, with a=4 as the center.

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