a) f(x) = x^2 - 16 = (x + 4)(x - 4) = 0 at x = 4 and x = -4
b) f(x) = x(100 - x) = 0 at x = 0 and x = 100
c) f(x) = 2x^2 - 11x + 12 = 0
For c) use quadratic formula x = (-b +- sqrt(b^2 - 4ac))/2a to get roots of c) or where f(x) = 0. You can also factor c) as f(x) = (2x - 8)(x - 3/2) = 0 at x = 4 and x = 3/2
Use the x-values for a) b) and c) to graph where the parabolas cross the x-axis...:)