1.

If a, b, c are in GP, prove that (a2 + b2 ), (ab + bc), (b2 + c2 ) are in GP.

Answer»

To prove: (a2 + b2 ), (ab + bc), (b2 + c2 ) are in GP 

Given: a, b, c are in GP 

Formula used: When a,b,c are in GP, b2 = ac

Proof: When a,b,c are in GP, b2 = ac … (i) 

Considering (a2 + b2 ), (ab + bc), (b2 + c2 ) (ab + bc)2 

= (a2b2 + 2ab2c + b2c2

= (a2b2 + ab2c + ab2c + b2c2

= (a2b2 + b4 + a2c2 + b2c2 ) [From eqn. (i)] 

= [b2 (a2 + b2 )+ c2 (a2 + b2 )] (ab + bc)2 = [(b2 + c2 ) (a2 + b2 )]

From the above equation we can say that (a2 + b2), (ab + bc), (b2 + c2) are in GP



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