Question

a) x-y=3
2x-y=9

b) x=3y
x+2y=10

Answer 1

$a) \\ \left \{ {{x-y=3} \atop {2x-y=9}} \right. \\ \\ x-y=3 \\ x=3+y \\ \\ substituindo , temos: \\ 2x-y=3 \\ 2(3+y)-y=3 \\ 6+2y-y=3 \\ 6+y=3 \\ y=3-6 \\ y=-3 \\ \\ x=3+y \\ x=3-3 \\ x=0$

$b) \\ \left \{ {{x=3y} \atop {x+2y=10}} \right. \\ \\ x+2y=10 \\ 3y+2y=10 \\ 5y=10 \\ y= \frac{10}{5} \\ y=2 \\ \\ substituindo, temos: \\ x=3y \\ x=3.2 \\ x=6$