Answer :

Let, S =


Using the properties of exponents:


The above term can be written as:



Denoting the terms in power with x,


We have-


S = 2x where x =


Clearly, we observe that x is neither possessing any common ratio or any common difference. But if you observe carefully you can see that numerator is possessing an AP and denominator of various terms are in GP


Many of similar problems are solved using the method of difference approach as solved below:


As x = …..Equation 1


Multiply both sides of the equation with 1/2,we have-



….Equation 2


Subtract equation 2 from equation 1,we have:



TIP: Make groups get rid of difference in the numerator




x =


Clearly, we have a progression with common ratio = 1/2


it is a Geometric progression


Sum of infinite GP = ,where a is the first term and r is the common ratio.


Note: We can only use the above formula if |r|<1


Clearly, a = and r =


x =


From equation 1 we have,


S = 2x = 21 = 2 = RHS


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