If x + 2y= 4 and xy = -8, what is the value of x^2 + 4y^2?
x + 2y = 4 square both sides
(x + 2y)^2 = 16
x^2 + 4xy + 4y^2 = 16 [xy = -8 ]
x^2 + 4(-8) + 4y^2 = 16
x^2 + 4y^2 - 32 = 16
x^2 + 4y^2 = 48
