# Thread: Changing the subject involving division (2)

1. ## Changing the subject involving division (2)

Hi, I thought I could do this last question in my exercise book but I have gone wrong somewhere. Could someone show me where please?

$f=\frac{uv}{u+v}$

$f(u+v)=uv$

$fu+fv=uv$

$fv=uv-fu$

$\frac{fv}{v-f}=u-u$

2. Originally Posted by Meggomumsie
Hi, I thought I could do this last question in my exercise book but I have gone wrong somewhere. Could someone show me where please?

$f=\frac{uv}{u+v}$

$f(u+v)=uv$

$fu+fv=uv$

$fv=uv-fu$

$\frac{fv}{v-f}=u-u$
In the 4th step you make a mistake;

$fv=uv-fu$

$fv=u(v-f)$

$\frac{fv}{v-f}=u$