Question

x+7=2y+1
3x-y=7

solve for x and y

Answer 1

{x+7=2y+1    ⇔  x-2y=1-7   ⇔ x-2y=-6

{3x-y=7     /*(-2)

{x-2y=-6

{-6x+2y=-14      (+)

x-6x-2y+2y=-6-14

-5x=-20     /:(-5)

x=4

x -2y=-6

4-2y=-6       /-4

-2y=-10     /:(-2)

y=5

Solution: (4; 5)