# Rearranging formula help

• November 7th 2008, 09:34 AM
natali.ferno
Rearranging formula help
hi ,

need some rearranging this formula

$\frac{1}{r} = \frac{1}{q} + \frac{1}{d}$

IF I want to make $r$ the subject of the formula, how would i go about this?
• November 7th 2008, 09:40 AM
Moo
Hello,
Quote:

Originally Posted by natali.ferno
hi ,

need some rearranging this formula

$\frac{1}{r} = \frac{1}{q} + \frac{1}{d}$

IF I want to make $r$ the subject of the formula, how would i go about this?

$\frac 1q+\frac 1d=\frac{d+q}{qd}$

So $\frac 1r=\frac{d+q}{qd}$

taking the inverse on both sides :

$r=\frac{qd}{q+d}$