Multiply and divide by 2.

Now,

Write the numerator as difference of the first and last term.i.e.

Write

and

and so on....

Now take the 1/2 common and:::

u get

which is

 Thnks...what book do u follow for these type of q for PCM?

I dont use any books to solve such questions....

I had seen my teacher solving a similar question using this technique in my coaching class....

And by the way ,

Will you please tell me what is latex?