Intermediate Algebra (6th Edition)

(9 + $x^{2}$)(9 - $x^{2}$)
81 - $x^{4}$ = (9 + $x^{2}$)(9 - $x^{2}$) Check by multiplying factors with FOIL: 9(9) + 9(-$x^{2}$) + $x^{2}$(9) + $x^{2}$(-$x^{2}$) =81 - 9$x^{2}$ + 9$x^{2}$ - $x^{4}$ = 81 - $x^{4}$