You have the equation:
y = -1/2 x + 1
In order to write the previous equation in the form Ax + By = C, proceed as follow:
y = -1/2 x + 1 multiply by 2 both sides
2y = -x + 2 add x both sides
x + 2y = 2
By comparing the previous equation with the form Ax + By = C, you can notice:
A = 1
B = 2
C = 2
Hence, the equation is:
x + 2y = 2