I have this equation $3-x-x^2$ which I want to convert into the form $a^2 - y^2$, so that then I can suppose $y$ = $a\sin\theta$, differentiate and then integrate it. But I can't convert that equation into this $a^2 - y^2$ form.
P.S. this is a homework question. My question here is not to solve this for me, but tell me how to do such (if there exists a formula) so that I may learn and prosper :)
EDIT: $a^2 - y^2$, in this equation $y$ may be anything which involves $x$ e.g. $(x-2)^2$