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If the first and the nth term of a G.P. are a ad b, respectively, and if P is the product of n terms, prove that P2 = (ab)n.

Given, the initial term of the G.P is an and the last term is

   

Hence,

The G.P.

   

is the place where r is the normal proportion.

Then, at that point,

   

Here,

   

is an A.P.

Furthermore, the result of

   

is given by,