Prove that the line through the point (x1, y1) and parallel to the line Ax + By + C = 0 is A (x – x1) + B (y – y1) = 0.
Let the slope of line Ax + By + C = 0 be m
Ax + By + C = 0
∴ m = -A/B
Equation of the line passing through point (x1, y1) and having slope is
∴ A(x – x1) + B(y – y1) = 0
So, the line through point (x1, y1) and parallel to the line Ax + By + C = 0 is A (x – x1) + B (y – y1) = 0