Question

se (x-y)^2- (x+y) = -20, então
x . y é igual a?

Answer 1

(x-y)² -(x +y) = -20
x² -2xy +y² -x -y = -20
-2xy +x +y = -20 ×(-1)
2xy -x -y = 20
xy -x -y = 20/2
xy -x -y = 10
xy = 10 +x+y