1.x⁴-1=（x^2+1)(x+1)(x-1)
2.x²+4x-xy-2y+4=(x+2)^2-y(x+2)=(x+2)(x-y+2)
3.4x²-12x+5=(2x-5)(2x-1)
4.21x²-31x-22=(21x+11)(x-2)
5.4x²+4xy+y²-4x-2y-3=(2x+y)^2-2(2x+y)-3=(2x+y-3)(2x+y+1)
6.9x^5-35x³-4x=x(9x^2+1)(x+2)(x-2)
7.3x²-6x=3x(x-2)
8.49x²-25=(7x+5)(7x-5)
9.6x²-13x+5=(3x-5)(2x-1)
10.x²+2-3x=(x+3)(x-1)
11.12x²-23x-24=(3x-8)(4x+3)
12.(x+6)(x-6)-(x-6)=(x-6)(x+5)
13.8x²-18=2((2x+3)(2x-3)
14.x²-(a-b)x-ab=x^2-(a-b)x+1/4(a-b)^2-1/4(a-b)^2-ab
=(x-1/2a-1/2b)^2-[1/2(a+b)]^2
=(x-1/2a-1/2b+1/2a+1/2b)(x-1/2a-1/2b-1/2a-1/2b)
=x(x-a-b)
15.x²+x+y²-y-2xy=(x-y)^2+x-y=(x-y)(x-y-1)
16.x²+x+y²-y-2xy=(x-y)(x-y-1)=99*(99-1)=9702
17.9x⁴+35x²-4=(x^2+1)(3x+2)(3x-2)
18.x²-y²-2yz-z²=x^2-(y+z)^2=(x+y+z)(x-y-z)