решите систему линейных уравненийспособом сложения 1) 2x-7y=8 x+3y=5 2) 3y-4x=8 y-5x=1 3) 2x-5y=2 3x-11=5 4) 2y-8x=1 5y+7x=3 5) 3x-4y=5 x+5y=-2 6) 2y-8x=5 y-3x=9

1). {2 x - 7 y = 8; {2 x - 7 y = 8;

{x + 3 y = 5; {2 x + 6 y = 10;

2 x - 7 y - 2 x - 6 y = 8 - 10;

- 13 y = - 2; y = 2/13;

2 x = 8 + 7 y; 2 x = 8 + 7 * 2/13; 2 x = 8 + 14/13; 2 x = 118/13; x = 59/13;

{x = 59/13; y = 2/13;

2). {3 y - 4 x = 8; {3 y - 4 x = 8;

{y - 5 x = 1; {3 y - 15 x = 3;

3 y - 4 x - 3 y + 15 x = 8 - 3; 11 x = 5; x = 5/11;

y = 1 + 5 x; y = 1 + 5 * 5/11; y = 1 + 25/11; y = 3 3/11;

{x = 5/11; y = 3 3/11;

3). {2 x - 5 y = 2; {6 x - 15 y = 6;

{3 x - 11 y = 5; {6 x - 22 y = 10;

6 x - 15 y - 6 x + 22 y = 6 - 10;

7 y = - 4; y = - 4/7;

2 x = 2 + 5 y; 2 x = 2 - 5 * 4/7; 2 x = 2 - 20/7; 2 x = - 6/7; x = - 3/7;

{x = - 3/7; y = - 4/7;

4). {2 y - 8 x = 1; {10 y - 40 x = 5;

{5 y + 7 x = 3; {10 y + 14 x = 6;

10 y - 40 x - 10 y - 14 x = 5 - 6;

- 54 x = - 1; x = 1/54;

2 y = 1 + 8 x; 2 y = 1 + 8 * 1/54; 2 y = 62/54; y = 31/54;

{x = 1/54; y = 31/54;

5). {3 x - 4 y = 5; {3 x - 4 y = 5;

{x + 5 y = - 2; {3 x + 15 y = - 6;

3 x - 4 y - 3 x - 15 y = 5 + 6;

- 19 y = 11; y = - 11/19;

x = - 2 - 5 y; x = - 2 - 5 * ( - 11/19); x = 17/19;

{x = 17/19; y = - 11/19;

6). {2 y - 8 x = 5; {2 y - 8 x = 5;

{y - 3 x = 9; {2 y - 6 x = 18;

2 y - 8 x - 2 y + 6 x = 5 - 18;

- 2 x = - 13; x = 6 1/2

y = 9 + 3 x; y = 9 + 3 * 13/2; y = 28 1/2;

{x = 6 1/2; y = 28 1/2.