1、(3x^2+ax+b)(2x^2-4x+5)=6x^4+(2a-12)x^3+(5+b-4a)x^2+(5a-4b)x+5b
乘积不含x^3与x的项,即：2a-12=0 5a-4b=0
解得 a=6 b=7.5
2、x^3-6x^3+13x^2-12x+k=（x^3+mx+n)^2
=x^6+2mx^4+m^2x^2+2nx^3+2nmx+n^2n 恒成立? 不可能!
3、6x^2-5xy-4y^2-11x+22y+m=(2x+y+k)(3x-4y+l)
=6x^2-5xy+(2l+3k)x-4y^2+(l-4k)y+kl 恒成立
则 2l+3k=-11 l-4k=22 kl=m
解得 m=-10 k=-5 l=2