大家给个指导,儿子的作业考住了他老爸

(2k-3)x+2x*x-3k
=2xk-3x+2x^2-3k
=(2x-3)k+2x^2-3x
值与k的取值无关
所以k的系数是0
所以2x-3=0
x=3/2
x*x+x-1=(3/2)*(3/2)+3/2-1=9/4+3/2-1=11/4
若4x^2+15x-5=0,求代数式(-15x^2-18x+9)-(-3x^2+19x-31)的值
(-15x^2-18x+9)-(-3x^2+19x-31)
=-15x^2-18x+9+3x^2-19x+31
=-12x^2-37x+40
=-3(4x^2+15x-5)+8x+25
=8x+25
4x^2+15x-5=0