第一题没看明白2、-n/n+1=-[(n+1)-1]/n+1=-1+1/(n+1) -n+1/n+2=-1+1/(n+2)1/(n+1) >1/(n+2) -n/n+1> -n+1/n+2-n+1/n=-1-1/n -n+2/n+1=-1-1/(n+1)1/n>1/(n+1) - 1/n<-1/(n+1)-n+1/n< -n+2/n+1
