[The jumpers]

2.ให้$f(x) = (x - a)(x - b)(?) + 4$
เเทน$x = c$จะได้$f(c) = (c - a)(c - b)(?) + 4 = 7$
$\left|\,(c - a)(c - b)(?)\right| = \left|\,3\right|$
$\therefore \left|\,c - b\right| = 1$