Jika f adalah fungsi kuadrat yang grafiknya melalui titik (-1, 0), (2, 0), dan (0, 2), maka nilai f (7) adalah....

(-1, 0) = (x1, 0)
(2, 0) = (x2, 0)
(0, 2) = (x, y)
Persamaan fungsi kuadrat
y = a(x - x1)(x - x2)
2 = a(0 - (-1)) (0 - 2)
2 = a (1)(-2)
2 = -2a
a = -1
y = a(x - x1)(x - x2)
f(x) = -1 (x + 1)(x - 2)
f(7) = -1 (7 + 1)(7 - 2) = -1 (8) (5) = -40