解3(a+b)²-27c²=3[(a+b)²-(3c)²]=3(a+b-3c)(a+b+3c) 16(x+y)²-25(x-y)²=[4(x+y)]²-[5(x-y)]²=[4(x+y)-5(x-y)][4(x+y)+5(x-y)]=(9y-x)(9x-y) a²(a-b)+b²(b-a)=a&#...