Ответы на вопрос:
1) {2x +3y= 2 {-2x + 5y = - 18 2x + 3y - 2x + 5y = 2 + (-18) 8y = -16 y = -16/8 y = - 2 2x + 3*(-2) = 2 2x - 6 =2 2x = 2 + 6 2x = 8 x= 8/2 x = 4 ответ: (4 ; -2) 2) { x+ 4y = 39 {2x - y = 15 |*4 {x + 4y = 39 {8x - 4y = 60 x+4y +8x -4y = 39+60 9x = 99 x= 11 11 + 4y = 39 4y = 39 - 11 y = 28/4 y = 7 ответ: (11 ; 7) №2. 1) {7x+2y = 9 {5x + 2y = 11 |*(-1) {7x +2y = 9 { - 5x - 2y = -11 7x + 2y - 5x - 2y = 9 - 11 2x = -2 x = -1 7*(-1) + 2y = 9 2y = 9 +7 2y = 16 y = 8 ответ: (-1 ; 8) 2) { 9x - 2y =-17 |*(-1) { x - 2y = 7 { - 9x + 2y = 17 { x - 2y = 7 - 9x +2y +x - 2y = 17 + 7 -8x= 24 x = 24 / (-8) x= 3 3 - 2y = 7 -2y = 7-3 -2y = 4 y = 4/(-2) y = -2 ответ: (3 ; - 2) 3) {x + 7y = 19 { x + 5y = 13 | *(-1) { x +7y = 19 { -x - 5y = -13 x + 7y - x - 5y = 19 - 13 2y = 6 y = 3 x + 7*3 = 19 x + 21 = 19 x = 19 - 21 x= -2 ответ : ( -2 ; 3). 4) {5х - 2у = 15 {2x - y = 7 |*(-2) {5x -2y =15 { -4x +2y = -14 5x -2y -4x +2y = 15-14 x = 1 5*1 - 2y = 15 -2y = 15-5 -2y = 10 y = -5 ответ : ( 1 ; -5).
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