The slope formula is what? (y2-y1)/(x2-x1). If we refer to the points of f(x+h), F(x), and such, "h" representing the distance between the first point and the second. Our ordered pairs will be seen as (x, f(x)) and (x+h, f(x+h)). By plugging in both ordered pairs to the formula, the result would be f(x+h)-f(x)/x+h-x. When we cancel the x's we would get: f(x+h)-f(x)/h and VOILA the difference quotient!