(3 -a)(3+a)(b+2a)(2a-b)(x²-1)(1+x²)
= (9 - a²)(b+2a)(2a-b)(x^2 - 1)(1 + x^2)
= (9 - a^2)(2ab - b^2 + 4a^2 - 2ab)(x^2 - 1)(1 + x^2)
= (9 - a^2)(4a^2 - b^2)(x^2 - 1)(1 + x^2)