Question

2x+y=-9
5x-2y=18
ну как на графике алгебра 7 класс

Answer 1

$\left \{ {{2x+y=-9} \atop {5x-2y=18}} \right. \left \{ {{y=-9-2x} \atop {5x-2y=18}} \right. \\ 5x-2(-9-2x)=18 \\5x+18+4x=18 \\5x+4x=0 \\9x=0 \\x=0 \\y=-9-2*0 \\y=-9-0 \\y=-9 \\(x,y)=(0,-9)$
Проверка:
$\left \{ {{2*0-9=-9} \atop {5*0-2*(-9)=18}} \right.\\ \\ \left \{ {{-9=-9} \atop {18=18}} \right.$