原式=(36x²+84x+49)(3x²+7x+4)-6
令a=3x²+7x+4
则36x²+84x+49=12a+1
原式=a(12a+1)-6
=12a²+a-6
=(3a-2)(4a+3)
=(9x²+21x+10)(12x²+28x+19)
=(3x+2)(3x+5)(12x²+28x+19)