11. It is customary to label the coordinates of the first point (x₁, y₁) and the coordinates of the second point (x2, Y2)

a. Write an expression to calculate the vertical change, Ay, of the line through these two points.

b. Write an expression to calculate the horizontal change, Ax, of the line through these two points.

c. Write an expression to calculate the slope of the line through these two points.​