1.

If a, b, c are in A.P. and a, b, d are in G.P., then prove that a, a – b, d – c are in G.P.

Answer»

a, b, c are in AP 

So, 2b = a + c …(1) 

b, c, d are in GP 

So, b2 = ad …(2) 

Multiply first equation with a and subtract it from 2nd. 

b2 – 2ab = ad – ac – a2 

a2 + b2 – 2ab = a(d – c) 

⇒ (a – b)2 = a(d – c) 

As a, (a – b), (d – c) satisfy the geometric mean relationship 

Hence a, (a – b),(d – c) are in G.P.



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