1.7х + 2у = 9 *(-1)
5х + 2у =11
-7x-2y=-9
5x+2y=11
2x=-2
5x+2y=11
x=-1
5*(-1)+2y=11
x=-1
y=8
2. 9х-2y=-17 I*(-1)
x-2y=7
-9x+2y=17
x-2y=7
-9x=17
x=7
-8x=24
х=3
3 - 2y = 7
-2y = 7-3
-2y = 4
y = 4/(-2)
y = -2
3. x+7y=19
x+5y=13 I*(-1)
x+7y=19
-x-5y=-13
x + 7y - x - 5y = 19 - 13
2y=6
y=3
x+21=19
x=19-21
x=-2
4. 5x-2y=15
2x-y=7 I*(-2)
5x-2y=15
-4x+2y=-14
5x-2y+4x+2y=-14+15
x=1
5*1 - 2y=15
-2y=15-5
-2y=10
y=-5