Đáp án:
a,(48x²+8x-1)(3x²+5x+2)-4
=[(48x²-4x)+(12x-1)][(3x²+3x)+(2x+2)]-4
=[4x(12x-1)+(12x-1)][3x(x+1)+2(x+1)]-4
=(12x-1)(4x+1)(x+1)(3x+2)-4
=[(12x-1)(x+1)][(4x+1)(3x+2)]-4
=(12x²+12x-x-1)(12x²+8x+3x+2)-4
=(12x²+11x-1)(12x²+11x+2)-4
+Đặt 12x²+11x-1 = a, ta có:
        a(a+3)-4
=a²+3a-4
=(a²-a)+(4a-4)
=a(a-1)+4(a-1)
=(a-1)(a+4)
⇔ (12x²+11x-1-1)(12x²+11x-1+4)
=(12x²+11x-2)(12x²+11x+3)