Question

se (x-y)2-(x+y)2=-20, Entao x.y e igual á?

Answer 1

Se (x-y)2-(x+y)2=-20

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

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

- xy - xy   = - 20

- 2xy = - 20(-1)

2xy = 20

xy = 10