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This question is actually from this years JEE Advance. The picture is of the sloution provided by this site. Can't really understand it. Please help out. I am in 11 so I may not be aware of the formula used or am just missing something. Sigma means adding but I somehow don't see that happening. Is there a shortcut or furmula for that?? Thanks!!

This question is actually from this years JEE Advance. The picture is of the sloution provided by this site. Can't really understand it. Please help out. I am in 11 so I may not be aware of the formula used or am just missing something. Sigma means adding but I somehow don't see that happening. Is there a shortcut or furmula for that??
Thanks!!

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Grade:11

1 Answers

Ajay
209 Points
6 years ago
Hi Ellish
Try to sum by putting k =1 to 13 , you see that that only first and last term remain while the terms in the middle get cancelled out.
 
 

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