2x²-5x-3=(x-3)(2x+1)
x -3
×
2x +1
-x²-2xy+15y²=(-x-5y)(x-3y)
-x -5y
×
x -3y
(a²+2a+3)²-13(a²+2a+3)+22 把(a²+2a+3)看成整体
=[(a²+2a+3)-2][(a²+2a+3)-11]
=(a²+2a+1)(a²+2a-8) 再分解
=(a+1)²(a+4)(a-2)