Question

Se x2+y2=13xy e xy=6, então o valor de (x+y)2 é ?

Answer 1

$x^2+y^2=13xy\\ x^2+y^2=13xy+0\\ x^2+y^2=13xy+\underbrace{2xy-2xy}_0\\ x^2+y^2+2xy=13xy+2xy\\ x^2+2xy+y^2=15xy\\ (x+y)^2=15xy, \ \ \ \ \ xy=6\\ (x+y)^2=15.6\\ (x+y)^2=\boxed{90}$

Answer 2

(6).2+(6).2
12+12: -24