第四题，求导数=(x-1)^3+(x+1)*3*(x-1)^2=(x-1)^2*[x-1+3x+3]=(x-1)^2*2[2x+1]令导数为0，得出x=1和-1/2x>-1/2，导数大于0x<-1/2，导数小于0
