2x^2-ax-y+6-2bx^2+3x-5y-1
=(2-2b)x^2+(3-a)x-y+6-5y-1
因为与x无关
所以
b=1
a=3
1/3*a^3-2b^2-1/4*a^3+3b^2=1/12*a^3+b^2
=(1/2)*3^3+1
=27/2+1
=14.5