# Math Help - subbing in x = (u+v)

1. ## subbing in x = (u+v)

came across this problem

$x^3+px=q$

sub in $x=u+v$

then it says they got this

$u^3+v^3+(3uv+p)(u+v) = q$ how did it become this? $x^3 \Rightarrow u^3+v^3$ this makes sense but the $(3uv+p)(u+v)$ doesn't. why isn't it just $p(u+v)$

2. ## Re: subbing in x = (u+v)

...

expand out $(u+v)^3$

3. ## Re: subbing in x = (u+v)

oh geez. maybe reading math this late at night is a bad idea. haha