分解因式
1. (a+b)^2-8(a+b)+16
解,得:
==[(a+b)-4]^2
==(a+b-4)^2
2. 9(a-b)^2-4(a+b)^2
解,得:
==[3(a-b)-2(a+b)][3(a-b)+2(a+b)]
==(3a-3b-2a-2b)(3a-3b+2a+2b)
==(a-5b)(5a-b)
3. (x-2y)^2-6(2y-x)(x+y)+9(x+y)^2
解,得:
== [(x-2y)-3(x+y)]^2
== (x-2y-3x-3y)^2
== (-5y-2x)^2
== (5y+2x)^2