# Thread: Quick explanation of integral

1. ## Quick explanation of integral

Hi,

How do you go from

double integral of (2r)/(1+r) drdtheta to:

2 times the double integral of (1-(1/(1+r)))drdtheta

2. Originally Posted by s7b
Hi,

How do you go from

double integral of (2r)/(1+r) drdtheta to:

2 times the double integral of (1-(1/(1+r)))drdtheta
$\displaystyle 2\int \frac{r}{1+r}dr=2\int \frac{1+r-1}{r+1}=2\int \frac{1+r}{1+r}+\frac{-1}{1+r}dr=2 \int 1-\frac{1}{1+r}dr$

you could also use polynomial long division