# Math Help - Rearranging formula help

1. ## 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?

2. Hello,
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 :

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