Question 167810
16x^4 - 40x^2 + 9
= 16x^4 - 36x^2 - 4x^2 + 9
= 4x^2(4x^2 - 9) - 1(4x^2 - 9)
= (4x^2 - 9)(4x^2 - 1)
= (2x + 3)(2x - 3)(2x + 1)(2x - 1)