(18) If a , b , c are in A.P then prove that (1/bc),(1/ca),(1/ab) are also in A.P

Solution:

a , b , c are in A.P

Divide each term by abc, so we get

(a/abc),(b/abc),(c/abc) are also an A.P

By simplifying this we get,

(1/bc),(1/ca),(1/ab) are also in A.P