2x2+xy-y2-4x+5y-6
=(2x-y)(x+y)-4x+5y-6
=(2x-y+2)(x+y-3)
x2-y2+a2-b2+2ax+2by
=(x-a)²-(y-b)²
=(x-a-y+b)(x-a+y-b)
3x2+5xy-2y2+x+9y-4
=(3x-y)(x+2y)+x+9y-4
=(3x-y+4)(x+2y-1)
b4-2b2-8
=(b²-4)(b²+2)
=(b-2)(b+2)(b²+2)