(a + 1)(a – 1)(a2 + 1) = ?
We know that,
From formula, (a + b)(a – b) = a2 – b2
(a + 1)(a – 1)(a2 + 1) = (a2 – 1)(a2+ 1)
Again applying the formula,
(a2 – 1)(a2+ 1) = (a2)2 – (12)2 = a4 – 1