Question

Minimize Q=x^2+2y^2, where x+y=3

Answer 1

The first step you need to do is to rewrite
x+y=3
as y=3-x
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
Hope this helps