6x²+xy-2y²=6x²-3xy+4xy-2y²=3x(2x-y)+2y(2x-y)=(2x-y)(3x+2y)
a⁴-5a²-36=a⁴-3a³+3a³-9a²+4a²-12a+12a-36=a³(a-3)+3a²(a-3)+4a(a-3)+12(a-3)=(a-3)(a³+3a²+4a+12)=(a-3)(a²+4)(a+3)
a²-b²+2bc-c²=a²-(b-c)²=(a-b+c)(a+b-c)
a⁴-b²-a³b-ab²=(a²-b)(a²+b)-ab(a²+b)=(a²+b)(a²-ab-b)
25y²-4x²+12x-9=25y²-(2x-3)²=(-2x+5y+3)(5y+2x-3)