Use this formula a2 − b2 = (a + b)(a − b)
(x+1)^2-(x-1)^2 in this case, a = x+1, b = x-1
= [(x+1) + (x-1)] * [(x+1) – (x-1)]
=(x +1 + x – 1) *(x +1 – x +1)
= 2x * 2
=4x
