f`(x)=-x^3+2x^2+2ax-2
f`(1)=0,a=1/2
f`(x)=-x^3+2x^2+x-2=-(x-1)(x^2-x-2)
=-(x+1)(x-1)(x-2)
f(-1)=-1/4,f(1)=-37/12,f(2)=-8/3
m取两较小极值之间范围
-37/12
f`(x)=-x^3+2x^2+2ax-2
f`(1)=0,a=1/2
f`(x)=-x^3+2x^2+x-2=-(x-1)(x^2-x-2)
=-(x+1)(x-1)(x-2)
f(-1)=-1/4,f(1)=-37/12,f(2)=-8/3
m取两较小极值之间范围
-37/12