1、4（a+b)²-(a-b)²
=[2(a+b)+(a-b)]*[2(a+b)-(a-b)]
=(3a+b)(a+3b)
2、-3xy-9y²-1/4x²
=-[(1/2x)^2+3xy+(3y)^2]
=-(1/2x+3y)^2
3、-a的四次方+8a²b²-16b的四次方
=-[a^4-8a^2b^2+16b^4]
=-(a^2-4b^2)^2
=-(a+2b)^2(a-2b)^2
4、(x²+y²)²-4x²y²
=(x^2+y^2+2xy)(x^2+y^2-2xy)
=(x+y)^2(x-y)^2