Question

Se (x+y) elevado a 2 -(x-y) elevado a 2 eh = a 20,entao xy e igual a quanto?

Answer 1

(x+y)^2 - (x-y)^2 = 20
x^2+2xy+y^2 - (x^2-2xy+y^2) = 20

x^2+2xy+y^2-x^2+2xy-y^2 = 20

4xy = 20
xy = 20/4
xy = 5