Question

maximize F=x^2+y^2 with
x + 2y = 10.

Answer 1

Are you using Lagrange multipliers?

Answer 2

no

Answer 3

Okay well clearly: \[
x = 10-2y
\]So \[
F(y) = (10-2y)^2+y^2
\]Find \(F'(y)\).