1){-4x+5y=20
{4X+3y=12
2){3Х+4y=24
{1,5x+y=-3
3){x+2y=-6
{x+2y=4

1)
-4х+5у=20
4х+3у=12,

5у=20+4х
у=(20+4х):5

4х+3((20+4х):5)=12
4х+3(4+4х)=12
4х+12+12х=12
16х=0
х=0, у=4

2)
3х+4у=24
1.5х+у=-3

у=-3+1.5х

3х+4(-3+1.5х)=24
3х-12+6х=24
9х=36
х=4, у=-9