A)
|y=2x+5
|2x+3y=31
|y=2x+5
|2x+3(2x+5)=31
2x+3(2x+5)=31
2x+6x+15=31
8x=16
x=2
y=2x+5
x=2
y=2*2+5
y=4+5
y=9
б)
|5x-7y=-24
|x=-3y+4
|5(-3y+4)-7y=-24
|x=-3y+4
5(-3y+4)-7y=-24
-15y+20-7y=-24
-22y=-44
y=2
x=-3y+4
y=2
x=-3*2+4
x=-6+4
x=-2
в)
|2x+5y=-8
|2x+3y=-4
|x=(-8-5y)/2
|2x+3y=-4
2x+3y=-4
2((-8-5y)/2)+3y=-4
(-16-10y/4)+3y=-4
-16-10y+12y=-16
2y=0
y=0
x=(-8-5y)/2
y=0
x=(-8)/2
x=-4