# Homework Help: Find the sum of the convergent series 4-2+1-1/2

1. May 18, 2010

### vipertongn

find the sum of the convergent series 4-2+1-1/2 ....

1. The problem statement, all variables and given/known data

find the sum of the convergent series . 4-2+1-1/2...

2. Relevant equations

sum of r^n |r|< 1 --> 1/(1-r)= sum

3. The attempt at a solution
4(1-1/2+1/4-1/8...)
I can see a pattern here where the denominator is going 2,4,8 so its like 1*2, 2*2, 2*2*2 but the 1 and + and the - throws me off...can someoen help me?

2. May 18, 2010

### Tedjn

Re: find the sum of the convergent series 4-2+1-1/2 ....

If this in fact is a geometric series, what would the common ratio be?

3. May 18, 2010

### Cyosis

Re: find the sum of the convergent series 4-2+1-1/2 ....

Hint: incorporate $(-1)^n$ to solve your sign problem.