1.5a平方2b(x-y)的六次方-30ab2(y-x)平方
=10a²b(x-y)^6-30ab²(x-y)²
=10ab(x-y)²[a(x-y)^4-3b]
2.（a-b）的三次方-（a-b）
=(a-b)[(a-b)²-1]
=(a-b)(a-b+1)(a-b-1)
3.(x平方+y平方)的平方-4x平方y平方
=[(x²+y²)-2xy][(x²+y²)+2xy]
=(x-y)²(x+y)²
4.x平方-2xy+y平方-9
=(x-y)²-9
=(x-y+3)(x-y-3)
已知a-b=3,b-c=-2,求a平方+b平方+c平方-ab-bc-ca的值
a-b=3,b-c=2
相加
a-c=5
原式=(2a²+2b²+2c²-2ab-2bc-2ac)/2
=[(a²-2ab+b²)+(b²-2bc+c²)+(c²-2ac+a²)]/2
=[(a-b)²+(b-c)²+(a-c)²]/2
=(9+4+25)/2
=19