There are two questions that I have no idea how to solve:
1. Let P, with coordinates(p,q) be a fixed point on the curve with equation y = mx + c and let Q, with coordinates (r,s), be any other point on y = mx + c. Use the fact that the coordinates of P and Q satisfy the equation y = mx + c to show that the gradient of the PQ is m for all positions of Q.
2. There are some values of a, b, and c for which the equation ax + by + c = 0 does not represent a straight line. Give an example of such values.