(a^2-4a)^2-(a^2-4a)-20
=[(a²-4a)-5][(a²-4a)+4]
=(a-5)(a+1)(a-2)²
x²+2xy+y²+x+y-6
=(x+y)²+(x+y)-6
=[(x+y)+3][(x+y)-2]
=(x+y+3)(x+y-2)第一题怎么没有？答好第一题马上采纳16m^2-16n^2+8m+1
=(16m²+8m+1)-16n²
=(4m+1)²-16n²
=(4m+1+4n)(4m+1-4n)