Question

o par (x,y) e a solução do sistema {x + y =20 , x - y = 6 o valor de x² - Y² É:

Answer 1

{x+y=20
{x-y=6
2x=26
x=26/2
x=13
x+y=20
13+y=20
y=20-13
y=7
x^2-y^2
(13)^2-(7)^2
169-49
120

Answer 2

$\left\{\begin{matrix}&1.&x+y=20\\&2.&x-y=6\end{matrix}\right\\\\\\\text{Desenvolvendo o produto de 1. com 2.:}\\\\(x+y)\cdot(x-y)=20\cdot6\\\\\boxed{x^2-y^2=120}$