Question

( х - у = 2, (2х - 3у = -1; (4х = -6у, (7у - 2х = 20; (8х - 3у = 7, (3х + у = 9;

Answer 1

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;