Algebra: A Combined Approach (4th Edition)

$(x^2+5)(x+2)(x-2)$
Given: $x^4+x^2-20 \\$ $1.)$ Let: $u=x^2$ $u^2+u-20$ $2.)$ Factor $u^2+u-20$ $(u+5)(u-4)$ $3.)$ Substitute $u=x^2$ $(x^2+5)(x^2-4)$ $4.)$ Factor $(x^2-4)$ $(x^2+5)(x+2)(x-2)$