代数式2x^2+ax-y+6-2bx^2+3x-5y-1的值与字母x的取值无关,
2-2b=0,b=1
a+3=0,a=-3
1/3a^3-2b^2-1/4a^3+3b^2
=-9-2+27/4+3
=-11+6+3+3/4
=-5/4