If a,b,c are in H.P., then ab+c, bc+a, ca+b will be in
(3)
Since, a,b,c are in H.P.
⇒ 1a,1b,1c are in A.P.
⇒ a+b+ca,a+b+cb,a+b+cc are in A.P.
⇒ 1+b+ca,1+a+cb,1+a+bc are in A.P.
⇒ b+ca,a+cb,a+bc are in A.P.
⇒ ab+c,bc+a,ca+b are in H.P.