Question

Write out the first three nonzero terms of the Taylor series for the following functions centered at the given point a. Then write the series using summation notation. f(x)=tan^{-1}4x,a=0

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asked 2021-01-02
Write out the first three nonzero terms of the Taylor series for the following functions centered at the given point a. Then write the series using summation notation.
\(f(x)=\tan^{-1}4x,a=0\)

Expert Answers (1)

2021-01-03
Given,
We have to find the Taylor series for the function \(f(x)=\tan^{-1}(4x)\) centered at a=0
Formula Used:
The general term for the Taylor Series \(f(x)=\sum_{n=0}^\infty\frac{f^n(a)}{n!}(x-a)^n\) centered at origin a.
Calculation: \(f(x)=\sum_{n=0}^\infty\frac{f^n(0)}{n!}(x)^n\)
\(=f(0)+xf'(0)+\frac{x^2}{2!}f''(0)+\frac{x^3}{3!}f'''(0)+...\)
Given the function \(f(x)=\tan^{-1}(4x)\)
\(f(x)=\tan^{-1}(4x)\Rightarrow f(0)=0\)
\(f'(x)=\frac{4}{1+16x^2}\Rightarrow f'(0)=4\)
\(f''(x)=-\frac{128}{(1+16x^2)^2}\Rightarrow f''(0)=0\)
\(f'''(x)=-\frac{128(1-64x+16x^2-1024x^3)}{(1+16x^2)^3}\Rightarrow f'''(0)=-128\)
...
Hence the Taylor series of the function \(f(x)=\tan^{-1}(4x)\) centered at 0 then
\(f(x)=f(0)=xf'(0)+\frac{x^2}{2!}f''(0)+\frac{x^3}{3!}f'''(0)+...\)
\(\tan^{-1}(4x)=0+x(4)+\frac{x^2}{2!}\times0+\frac{x^3}{3!}\times(-128)+...\)
\(\tan^{-1}(4x)=4x-128\frac{x^3}{3!}+...\)
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