If in a triangle ABC, the altitudes from the vertices upon the opposite sides are in H.P. then sin A, sin B, sin C are in
The three altitudes
AD, BE and CF are c sinB, a sinC, b sinA which are in H.P. or sinBsinC,sinCsinA,sinAsinBare in H.P.
or 1sinBsinC,1sinCsinA,1sinAsinB are in A.P.
or sinA,sinB,sinC are in A.P.
We have multiplied each term by sinAsinBsinC.