2x²+ax-y+6-2bx²+3x-5y-1
=2(1-b)x²+(a+3)x-6y+5
a=-3 b=1
(1/3)a³-2b²-（1/4）a²+3b²+2b²
=(1/12)a³+3b²
= (1/12)(-3)³+3*1²
=-27/12+3
=-9/4+12/4
=3/4