If 
are in A.P., prove that:
bc, ca, ab are in A.P.
Since, bc, ca, ab are in A.P.
= 
= 
Since, 
are in A.P.
Multiply in both denominator and numerator with,
C in LHS and a in RHS
Hence given terms are in AP
4
If are in A.P., prove that:
bc, ca, ab are in A.P.
Since, bc, ca, ab are in A.P.
=
=
Since, are in A.P.
Multiply in both denominator and numerator with,
C in LHS and a in RHS
Hence given terms are in AP