1.Решите систему уравнений способом сложения: 1){2x + 3y = 2 {-2x + 5y = -18 2){x + 4y =...

$1)\left \{ {{2x + 3y = 2} \atop {-2x + 5y = -18} \right.\\ 2x+(-2x)+3y+5y=2+(-18)\\ 2x-2x+3y+5y=2-18\\ 8y=-16\\ y=-2\\ \\ 2x+3*(-2)=2\\ 2x-6=2\\ 2x=2+6\\ 2x=8\\ x=8:2\\ x=4$

Ответ: (4; -2)

$2)\left \{ {{x + 4y = 39 } \atop {2x - y = 15 \ |*4}} \right.\\ \\ \left \{ {{x+4y=39 } \atop {8x - 4y = 60}} \right.\\ \\ x+8x+4y-4y=39+60\\ 9x=99\\ x=11\\ \\ 11+4*y=39\\ 4y=39-11\\ 4y=28\\ y=7$

Ответ: (11; 7)

$3) \left \{ {{x + 7y = 19} \atop {x + 5y =13 \ |*(-1)}} \right.\\ \\ \left \{ {{x + 7y = 19} \atop {-x - 5y =-13 }} \right.\\ \\ x+(-x)+7y+(-5y)=19+(-13)\\ x-x+7y-5y=19-13\\ 2y=6\\ y=3\\ \\ x+7*3=19\\ x+21=19\\ x=19-21\\ x=-2$

Ответ: (-2; 3)

$4)\left \{ {{5x - 2y = 15} \atop {2x - y = 7 \ |*(-2)} \right.\\ \\ \left \{ {{5x - 2y = 15} \atop {-4x +2 y = -14 } \right.\\ \\ 5x-4x-2y+2y=15-14\\ x=1\\ \\ 5*1-2y=15\\ 5-2y=15\\ -2y=15-5\\ -2y=10\\ y=-5$

Ответ: (1; -5)