(6)(x+1)(x+2)(x+3)(x+4)-24(7)(x-3y)^2+x^2-6xy+9y^2-2(8)(2x-5y)(2x-5y+4)-21因式分解是十字相乘法吗？？？

Question

(6)(x+1)(x+2)(x+3)(x+4)-24
(7)(x-3y)^2+x^2-6xy+9y^2-2
(8)(2x-5y)(2x-5y+4)-21
因式分解
是十字相乘法吗？？？

Answer 1

(x+1)(x+2)(x+3)(x+4)-24
=(x+1)(x+4)(x+2)(x+3)-24
=(x^2+5x+4)(x^2+5x+6)-24
=(x^2+5x)^2+10(x^2+5x)+24-24
=(x^2+5x)(x^2+5x+10)
(x-3y)^2+x^2-6xy+9y^2-2
=(x-3y)^2+(x-3y)^2-2
=2[(x-3y)^2-1]
=2(x-3y+1)(x-3y-1)
是的啊 不懂问我!
(2x-5y)(2x-5y+4)-21
=(2x-5y)^2+4(2x-5y)-21
=(2x-5y+7)(2x-5y-3)