Find series given values of derivatives

boomer22
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Homework Statement


All you know about a function f[x] is:
f[0]=2, f '[0]=6, and f ''[0]=-8.
Write down the expansion of f[x] in powers of x through the x^2 term


Homework Equations


none


The Attempt at a Solution



I think the answer is 2 + 6x - 4x^2 , I just don't have any way to check so I want someone to confirm this.
 
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What you've written down certainly works.
 
morphism said:
What you've written down certainly works.

thanks a lot
 
boomer22 said:

Homework Statement


All you know about a function f[x] is:
f[0]=2, f '[0]=6, and f ''[0]=-8.
Write down the expansion of f[x] in powers of x through the x^2 term


Homework Equations


none


The Attempt at a Solution



I think the answer is 2 + 6x - 4x^2 , I just don't have any way to check so I want someone to confirm this.

You certainly can check it yourself! If f(x)= 2+ 6x- 4x2, what is f(0)? What is f'(0)? What is f''(0)?
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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