Inactive Tutor answered 09/17/13
Tutor
New to Wyzant
Rewrite the equation in slope-intercept form, y = mx + b, where m is the slope and b is the y value of the y intercept. Then, the slope is the change in the y values divided by the change in the x values.
m = (y2 - y1)/(x2 - x1) = [(mx2 + b) - (mx1 + b)]/(x2 - x1)
But, this is just [m(x2 - x1) + (b - b)]/(x2 - x1), or
m(x2 - x1)/(x2 - x1) = m