If x + 2y= 4 and xy = 8, what is the value of x^2 + 4y^2?
x + 2y = 8 square both sides
x^2 + 4xy + 4y^2 = 64
x^2 + 4(8) + 4y^2 = 64
x^2 + 4y^2 = 64 - 4(8)
x^2 + 4y^2 = 32
