1.(x+3y)²+（2x+6y）（3y-4x）+（4x-3y）²
=(x+3y)²-2(x+3y)(4x-3y）+（4x-3y）²
=(x+3y-4x+3y)²
=(3x-6y)²
=9(x-2y)².
2.a四次方-6a²-27
=(a²+3)(a²-9)
=(a²+3)(a+3)(a-3).
3.—56x³yz+14x²y²z－21xy²z²
=-7xyz(8x²-2xy+3yz).
4.5m（x-y）²+10n（y-x）³
=5（x-y)²(m+2n(y-x))
=5（x-y)²(m+2ny-2nx).