Question

Решите систему уравнения 3 способами:графического,методам подстановки, и обычный.
9x+4y=-2
x+y=-8

Answer 1

$1) \left \{ {9x+4y=-2, } \atop {x+y=-8;}} \right. \ \ \ \left \{ {y= \frac{-9x-2}{4} , } \atop {y=-x-8;}} \right. \ \ \ \left \{ {x=6, } \atop {y=-14;}} \right. \\ (6;-14).$
$2) \left \{ {9x+4y=-2, } \atop {x+y=-8;}} \right. \ \ \ \left \{ {x=-y-8, } \atop {9(-y-8)+4y=-2;}} \right. \\ -9y-72+4y=-2, \\ -5y=70, \\ y=-14, \\ x=-(-14)-8, \\ x=6, \\ \left \{ {x=6, } \atop {y=-14;}} \right. \\ (6;-14).$
$3) \left \{ {9x+4y=-2, } \atop {x+y=-8;}} \right. \ \ \ \left \{ {9x+4y=-2, } \atop {-4x-4y=32;}} \right. \\ 9x-4x=-2+32, \\ 5x=30, \\ x=6, \\ 6+y=-8, \\ y=-14, \\ \left \{ {x=6, } \atop {y=-14;}} \right. \\ (6;-14).$