Решите систему уравнение 8х+2у=7
4х-у=9

$left { {{-y=9 - 4x} atop {8x + 2y = 7}} right.$

$left { {{y=4x - 9} atop {8x + 2(4x-9) = 7}} right.$

$left { {{y=4x - 9} atop {8x+8x-18 = 7}} right.$

$left { {{y=4x - 9} atop {16x = 7 + 18}} right.$

$left { {{y=4x - 9} atop {16 x = 25}} right.$

$left { {{y=4*1 frac{9}{16} - 9} atop {x=1 frac{9}{16} }} right.$

$left { {{y=-2,75} atop {x=1 frac{9}{16} }} right.$

Проверка:

$4 * ( frac{25}{16} ) + 2,75 = 9$

$8 * frac{25}{16} + 2*(-2,75) = 7$