解
81x的4次方-18x²y²+y的4次方
=(9x²-y²)²
=(3x-y)²(3x+y)²
(a+b)²-2(a+b)c+c²
=[(a+b)-c]²
=(a+b-c)²
20a²b²-20ab+5
=5(4a²b²-4ab+1)
=5(2ab-1)²
3a(x²+4)-48ax²
=3a[(x²+4)-16x²]
=3a(x²-4x+4)(x²+4x+4)
=3a(x-2)²(x+2)²