wat is method of diffrence ??plz explain how n where to use it ??

Hello mohit

Your question is exactly not clear to me..but then also i am attempting it...if you understand by this ..then i will feel happy..else make it a bit more clear please...

Some times a series is exactly in AP like..

1   3    5     7     9    11    13     15  ...............this is an AP with C.D = 2

But when

1    4    9   16   25...............................  then this is not an AP ....but when u see it clearly..then difference between two terms are in AP

1    4    9   16   25...............................

    3    5   7    9     .........................

So to solve such type of Question...we use this method...

S =  1    4    9   16   25...............................Tn 

S =        1    4    9   16   25.........................Tn-1  Tn

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0  = (1  + 3 + 5 + 7+9 +........n terms ............) - Tn

Tn =  n^2

So once you find Tn ..then u can easily find out the sum ...by applying  sigma (Tn)  and apply limit as required

I hope this help you

Yagya

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