# Power series. tell me if i'm on the right track.

1. Jan 7, 2009

### crazyformath2

I have to find the power series f(x)= 3 / (2 -5x).

I devided everything by 2 so I have (1/2) / (1 - 5x/2) = $$\sum$$ ar^n

and then through some steps I have 15x^n / 2^n+1

and I on the right track? How do I find the interval of convergence?

2. Jan 7, 2009

### sutupidmath

$$f(x)=\frac{3}{2-5x}=\frac{3}{2}*\frac{1}{1-\frac{5x}{2}}=\frac{3}{2}\sum_{n=0}^{\infty}[\frac{5}{2}x]^n$$

To find the radius of convergence u might want to use the ratio test.

Last edited: Jan 7, 2009
3. Jan 7, 2009

### crazyformath2

shouldnt that 5/2 x be negative though? does that make a difference?