1){x-y=2 ⇒x=2+y
{2x-3y=-1
2(2+y)-3y=-1;
4+2y-3y=-1;
-y=5;
y=5; x=2+5=7;
2){4x=-6y ⇒x=-6/4y=-1.5y;
{7y-2x=20
7y-2(-1.5y)=20;
7y+3y=20;
10y=20;
y=20/10=2;
x=-1.5·2=-3;
3){8x-3y=7
{3x+y=9; ⇒y=9-3x;
8x-3(9-3x)=7;
8x-27+9x=7;
17x=34;
x=34/17=2;
y=9-6=3;
= -36х-2,4у-14у+42х=6х-16,4у=6*(-3,1)-16,4*0,3= -18,6-4,92= -23,52