The slope between two points is calculated by the rate of change in (y)-coordinate values by the rate of change in (x)-coordinate values.
For example, the slope between the points (Pleft({14,10} right)) and (Qleft({15, - 6} right)) is equal to (m = frac{{ - 6 - 10}}{{15 - 14}} = - frac{{16}}{1} = - 16).