几道数学计算题(要用十字相乘法作,
1.x2-11x+18
2.4m2-12m+9
3.5+7x-6x2
4.12x2+xy-6y2
5.x2-4x+____=(x+3)(x+_____)
6.若x2+ax+b=(x+2)(x-4)则a=_____,b=________
7.a3-5a2b+6ab2
8.2y2-4y-6