Question

{x=5y
x+y=12

{x-y=10
{2x+3y=10

{x+y=3
12x-9y=-20

Answer 1

x=5y
x+y=12
5y+y=12
6y=12
y=2

x-y=10
2x+3y=10
x=y+10
2(y+10) + 3y=10
2y+20+3y=10
5y=10-20
y=-10/5
y=-2

x+y=3
12x-9y=-20
x=-y+3
12(-y+3)-9y=-20
-12y+36-9y=-20
-21y=-20-36
y=-56/-21
y=56/21

Answer 2

1° y=2 x=10 2°x=8 y=-2 3°x=2 y=1