There seems to be a printing mistake here
If there are (2n−1) terms instead of (2n+1) terms then nth terms of the A.P., G.P. and H.P. are the A.M., G.M. & H.M of the first and the last terms.
So, a≥b≥c&ac−b2(B,D)
otherwise if there are (2n+1) terms then the nth terms should be in decreasing order of A.P.,G.P. & H.P.
i. e.a≥b≥c(B)