解
-15a³b²+9a²b²-3ab³
=-3ab²(5a²-3a+b)
(x²+1)²-4x²
=(x²+1)²-(2x)²
=(x²+1-2x)(x²+1+2x)
=(x-1)²(x+1)²
81(a+b)²-16(a-b)²
=[9(a+b)-4(a-b)][9(a+b)+4(a-b)]
=(9a+9b-4a+4b)(9a+9b+4a-4b)
=(5a+13b)(13a+5b)
(a²+2a)²+2(a²+2a)+1
=[(a²+2a)+1]²
=(a+1)的4次方