# Homework Help: High school Calculus homework on series

1. Mar 9, 2010

### snowlove

high school Calculus B/C class homework:

1) Find a Series for f(x) = $$\frac{1}{1+x}$$ then find the interval of convergence.

i know that $$\frac{1}{1+x}$$ = 1-x+ $$x^{2}$$-$$x^{3}$$+...+ $$-x^{n}$$+.... -1<x<1
but then i don`t understand how can i use the result from 1) to find 2) answer? since you guy will teach me how to do 2) then do i just do the same thing for 3) ?

2) Using your result from 1) find a series for $$\frac{1}{1+x^2}$$

3) Using your result from 2) find a series for $$tan^{-1}x$$ then use your series to approximate $$\pi$$ to four decimal places. How many terms did you need?

Last edited: Mar 9, 2010
2. Mar 9, 2010

### rock.freak667

Re: series

Replace x by x2

For the third one, consider what d/dx(tan-1x) gives

Last edited: Mar 9, 2010
3. Mar 9, 2010

Re: series

thank you