Question

решите систему уравнений
4x-y=9
3x+7y=-1

Answer 1

4x-y=9/*7⇒28x-7y=63
3x+7y=-1
31x=62
x=2
y=4*2-9=8-9=-1
(2;-1)

Answer 2

$\left \{ {{4x-y=9} \atop {3x+7y=-1}} \right. = \left \{ {{y=4x-9} \atop {3x+7y=-1}} \right.\\3x+7(4x-9)=-1\\ 3x+28x-63=-1\\31x=-1+63\\x=62:31\\x=2\\\\y=4*2-9\\y=-1$