y=x^3+mx^2+nx+q
y'=3x^2+2mx+n
x=-1,3*(-1)^2+2m*(-1)+n=0,3-2m+n=0 .(1)
x=2,3*2^2+2m*2+n=0,12+4m+n=0 .(2)
(2)-(1):9+6m=0,m=-3/2,n=2m-3=-3-3=-6
m=-3/2,n=-6
y'=3x^2-3x-6=3(x^2-x-2)=3(x+1)(x-2)
当X属于[-1,2],Y'