# Chapter R - Section R.4 - Factoring Polynomials - R.4 Exercises: 71

A. ($x^{2}$ - 1)($x^{2}$ + 1)

#### Work Step by Step

$x^{4}$ - 1 is a difference of squares, for which $x^{2}$ - $y^{2}$ = (x + y)(x - y), so the expression factors to ($x^{2}$ - 1)($x^{2}$ + 1). We can also use FOIL to check.

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