(x^2+4x+16)(x^2+9x+16)-6x^2
=[(x²+16)+4x][(x²+16)+9x]-6x²
=(x²+16)²+13x(x²+16)+36x²-6x²
=(x²+16)²+13x(x²+16)+30x²
=[(x²+16)+10x][(x²+16)+3x]
=(x²+10x+16)(x²+3x+16)