If a1, a2, a3.....an are in H.P., then a1a2+a3+......an . a2a1+a3+.....+an,...... ana1+a2+.......+an−1
are in
H.P.
a1, a2, a3 ...........an are in H.P. 1a1, 1a2, 1a3................ 1an are in A.P.
Multiply each term by a1 + a2 + a3 .........+ an then substract 1 from each term
We get a2+a3+.........+ana1, a1+a3+.......+ana2, ........... a1+a2+..........+an−1an are in A.P.
∴ a1a2+a3+........+an, a2a1+a3+...........+an, ........... ana1+a2+........+an−1 are in H.P.