(3)5ax+7ay-5bx-7by
=5ax-5bx+7ay-7by
=5x(a-b)+7y(a-b)
=(a-b)(5x+7y)
(4)x的立方y(tǒng)+3x-2x的平方y(tǒng)的平方-6y
=x³y-2x²y²+3x-6y
=x²y(x-2y)+3(x-2y)
=(x-2y)(x²y+3)
(5)6ax+15b的平方y(tǒng)的平方-6b的平方x-15ay的平方
=6ax-6b²x-(15ay²-15b²y²)
=6x(a-b²)-15y²(a-b²)
=3(a-b²)(2x-5y²)
(6)7x的平方-3y+xy-21x
=7x²-21x+xy-3y
=7x(x-3)+y(x-3)
=(x-3)(7x+y)
(7)3a的平方+bc-3ac-ab
=3a²-3ac+bc-ab
=3a(a-c)-b(a-c)
=(a-c)(3a-b)
(8)a的平方m+bn-an-abm
=a²m-abm+bn-an
=am(a-b)-n(a-b)
=(a-b)(am-n)
(9)x的平方-a的平方-2x-2a
=(x+a)(x-a)-2(x+a)
=(x+a)(x-a-2)
(10)4a的平方-12ab+9b的平方-25
=(2a-3b)²-5²
=(2a-3b+5)(2a-3b-5)
(11)4x的平方-4xy+y的平方-a的平方
=(2x-y)²-a²
=(2x-y+a)(2x-y-a)
(12)1-m的平方-n的平方+2mn
=1²-(m-n)²
=(1+m-n)(1-m+n)
(13)a-a的立方
=a(1-a²)
=a(1+a)(1-a)
(14)x的立方y(tǒng)-xy的立方
=xy(x²-y²)
=xy(x+y)(x-y)
(15)4x的立方y(tǒng)的立方-9xy
=xy(4x²-9)
=xy(2x+3)(2x-3)
(16)4x的平方-8x-12y-9y的平方
=4x²-9y²-8x-12y
=(2x+3y)(2x-3y)-4(x+3y)
=(2x+3y)(2x-3y-4)