（1）-4a³b²+6a²b³-6ab²
=-2ab²(2a²-3ab+3)
（2）4x²y²-x²
=x²(4y²-1)
=x²(2y+1)(2y-1)
（3）（x-2y）²+6(2y-x)+9
=（x-2y）²-6(x-2y)+9
=(x-2y-3)²
(4)121(a+b)²-25（a-b）²
=[11(a+b)+5(a-b)][11(a+b)-5(a-b)]
=(16a+6b)(6a+16b)
=4(8a+3b)(3a+8b)