Question

Resolva Os Problemas x+2y = 1200
x-2y = 400

Answer 1

X+2y=1200

X-2y=400 // x=400+2y

(400+2y) +2y= 1200

2y+2y=1200-400

4y= 800

Y=800/4

Y=200

X=400+2y

X= 400 +2.(200)

X=800

Answer 2

$\begin{cases}x+2y=1200\;\;\;\Rightarrow x = 1200-2y\\x-2y=400 \hspace{1cm} x =1200-2\times 200 \Rightarrow\\\end{cases}\\\text{} \hspace{3.25cm}x = 1200-400\\x-2y=400\hspace{1.25cm}\boxed{x = 800}\\1200-2y-2y=400\\-4y=400-1200\\-4y=-800\\y=\dfrac{-800}{-4}\\\boxed{y=200}$

Espero ter sido útil