<span>The first step you need to do is to rewrite x+y=3 as y=3-x </span><span>Now we can replace the y in the equation with our newfound value for y, which is y=3-x. So lets write it now like this Q=x^2+2(3-y)^2
=x^2+18-12x+2x^2 =3x^2+18-12x </span>Hope this helps
