Question

X+Y=4
X-Y=12

Qual o valor das equações?

( ) x= - 4 e y = 8
( ) x= 8 e y = 4
( ) x= 8 e y = - 4
( ) x= - 8 e y = -4

Answer 1

Resposta:

$\left \{ {{x+y=4} \atop {x-y=12}} \right. \\\\\left \{ {{x=4-y} \atop {4-y-y=12}} \right. \\\\\left \{ {{x=4-y} \atop {-2y=12-4}} \right. \\\\\left \{ {{x=4-y} \atop {-2y=8}} \right. \\\\\left \{ {{x=4-y} \atop {y=-\frac{8}{2} }} \right. \\\\\left \{ {{x=4-y} \atop {y=-4 }} \right. \\\\\left \{ {{x=4-(-4)} \atop {y=-4 }} \right. \\\\\left \{ {{x=4+4} \atop {y=-4 }} \right. \\\\\left \{ {{x=8} \atop {y=-4 }} \right.$

a alternativa correta: C

Explicação passo-a-passo: