x-3 x+3 12x
E(x) = --------- - --------- + ----------
x+3 3-x x²-9
(x-3)² (3-x)(x-3) 12x
E(x) = ----------------- + ----------------- + ----------------
(x+3)(x-3) (x+3)(x-3) (x+3)(x-3)
x²+9-6x+9-x²+12x
E(x) = --------------------------
(x+3)(x-3)
6x+18 6(x+3)
E(x) = ---------------- = --------------
(x+3)(x-3) (x+3)(x-3)
6
E(x) = -------
x-3