2X²-5X-12 7X²-19X-6X²Y²+2XY-8X²+2XY-8Y²

2X²-5X-12 7X²-19X-6X²Y²+2XY-8X²+2XY-8Y²
2X²-5X-12
7X²-19X-6
X²Y²+2XY-8
X²+2XY-8Y²

2X²-5X-12 7X²-19X-6X²Y²+2XY-8X²+2XY-8Y²
2X²-5X-12 =(2x+3)(x-4) 十字相乘
7X²-19X-6=(7x+2)(x-3) 十字相乘
X²Y²+2XY-8=(xy-2)(xy+4) 十字相乘
X²+2XY-8Y²
=X²+2XY+Y²-9Y²
=(X+Y)²-9Y²
=(X+Y-3Y)(X+Y+3Y)
=(X-2Y)(X+4Y)

2X²-5X-12=（2x+3）（x-4）
7X²-19X-6=（7x+2）（x-3)
X²Y²+2XY-8=(xy-2）（xy+4)
X²+2XY-8Y²=（x-2y)(x+4y)