Question

Boa tarde qual o resultado desse sistema?

Answer 1

x + y = 7 → x = 7 - y

3 ( y - x ) = - 9

3 ( y - 7 + y ) = - 9

6y - 21 = - 9

6y = - 9 + 21

y = 12/6

y = 2

x = 7 - y

x = 7 - 2

x = 5

Answer 2

$\left \{ {{x+y=7} \atop {3(y-x)=-9}} \right.$

$y=7-x$

$3(7-x-x)=-9$

$-6x +21 = -9$

$-6x=-21-9$

$x=\frac{30}{6}=5$

$x+y=7$

$5+y=7$

$y=2$

x=5 e y=2