①3a(x-y)+9(y-x)②16mn^4-m③(x-y)³+9(x-y)+6(x-y)²④(x+

1.
3a(x-y)+9(y-x)
=3a(x-y)-9(x-y)
=3(x-y)(a-3)
2.
16mn⁴-m
=m(16n⁴-1)
=m(4n²+1)(4n²-1)
=m(4n²+1)(2n+1)(2n-1)
3.
(x-y)³+9(x-y)+6(x-y)²
=(x-y)[(x-y)²+6(x-y)+9] /后一个括号内将x-y看做整体,运用完全平方公式
=(x-y)(x-y+3)²
4.
(x+2)(x+4)+2x²-5
=x²+6x+8+2x²-5
=3x²+6x+3
=3(x²+2x+1)
=3(x+1)²