4x=y
2x^2 -y =0 so than we substitute the y value from the first equation inside second equation in place of y we get
2x^2 -4x =0 than we solve it for x we get
2x^2 -4x =0
2x(x-2) =0
2x =0
x_1 = 0
x - 2 =0
x_2 = 2
so for x_1 = 0 result y_1 = 4*0 = 0 so the solution set will be (0,0)
and in case of x_2 = 2 result y_2 = 4*2 = 8 so the sol. set will be (2,8)
hope this will help you