soluzione Scomporre     9 - 4x2 + (2x + 3)(4x + 5) = = (3 - 2x)(3 + 2x) + (2x + 3)(4x + 5) = = (2x + 3) [(3 - 2x) + (4x + 5)] = = (2x + 3)(2x + 8) = = 2(2x + 3)(x + 4) = = 2(x + 4)(2x + 3)