Question

x+y=3

x-y=9

 preciso resolver isto pelo metodo da substituiçao

 

Answer 1

$\left \{ {{x+y=3} \atop {x-y=9}} \right. =>\boxed{x=3-y}\\\\3-y-y=9\\3-2y=9\\-2y=6(-1)\\2y=-6\\y=\frac{-6}{2}\\\\\boxed{\boxed{y=-3}}\\\\x+y=3\\x+(-3)=3\\x-3=3\\x=3+3\\\\\boxed{\boxed{x=6}}$