Question

решите систему уравнений : 4х – у = 9; 3х + 7у = - 1.

Answer 1

4x-y=9
4x=9+y
x=(9+y)/4
3×(9+y)/4+7y=-1
(27+3y)/4+7y=-1
(27+3y+28y+4)/4=0
27+3y+28y+4=0
31y+31=0
31y=-31
y=-1
3x+7×(-1)=-1
3x-7=-1
3x=-1+7
3x=6
x=2