19. Let f(x) = x + 1 and define s(x) to be the slope of the line through the points (0,0) and (x, f(x) ), as shown below. For example, s(2) = slope of the line through (0,0) and (2,3) = 3. (a) Evaluate s(1), s(3) and s(4). (b) Find a formula for s(x). y = x+l ( X, X+1 ) - - s(x) = slope = 2 3 4 X