Using the relations
r1 = S/(s-a) where S = area and s is semi-perimeter.
r2 = S/(s-b)
r3 = S/(s-c).
As the radii are in HP their reciprocals are in A.P.
So (s-a)/S,..,.. are in AP or s-a, s-b, s-c are in AP so a,b,c are in AP
Hence A is the correct answer
Thanks & Regards
Jitender Singh
IIT Delhi
askIITians Faculty