解(2x²+ax-y+6)-(2bx²-2x+5y-1)=(2-2b)x²+(a+2)x-6y+7∵取值与x无关∴2-2b=0 a+2=0∴b=1，a=-2∴1/2a²-2b²+4ab=1/2×4-2+4×1×(-2)=2-2-8=-8
