解
2x²+ax-y+6-(2bx²-3x+5y)
=(2x²-2bx²)+(ax+3x)-6y+6
=(2-2b)x²+(a+3)x-6y+6
与x值无关
∴2-2b=0.a+3=0
∴a=-3.b=1
∴1/3a³-2b²-(-1/4a³-2b²)
=(1/3a³+1/4a³)+(-2b²+2b²)
=7/12a³
=7/12×(-27)
=-63/4