Question

已知代数式2x^2+ax-y+6-2bx^2+3x+y-1的值与字母的取值无关，求1/3a^3-2b^2-1/4a^3+3b^2的值

Answer 1

整理原式得：(2-2b)x^2+(a+3)x+5
与字母的取值无关说明，x^2与x的系数均为零
即可得：2-2b=0
a+3=0
得：b=1
a=-3
代入得：-5/4
答:1/3a^3-2b^2-1/4a^3+3b^2的值为-5/4。

Answer 2

2x^2+ax-y+6-2bx^2+3x+y-1
=(2-2b²)x+(a+3)x+5
值与字母的取值无关，则
2-2b²=0,a+3=0
解得b²=1，a=-3
1/3a^3-2b^2-1/4a^3+3b^2
=1/12a³+b²
=1/12×(-3)³+1
=-9/4+1
=-5/4