Question

solutia sistemului 3x-y=4, x+y=0

Answer 1

y=3x-4
x+3x-4=0
4x=4
X=1
y=-1

Answer 2

$\displaystyle \left \{ {{3x-y=4} \atop {x+y=0}} \right \\ ------ (+)\\ \ 4x \ \ \ \ |\ \ \ \ \ 4 \\ x=1 \\ \\ 1+y=0 \\ y=-1$