Sum of finite series

• Apr 1st 2009, 12:05 PM
champrock
Sum of finite series
What is the value of

1*2 / 3! + (2*2^2)/4! + (3*2^3)/5! ............... (15*2^15)/17!

I tried making a general term for this but was unable to proceed further with that method. Secondly I multiplied the sum by 2 and tried to subtract it from the original (AP-GP sort of a method) but that is also not taking me any further.

Thanks
• Apr 1st 2009, 06:35 PM
Schung
You can first use 17! as denominator. You can then find that it is a very standard AP and GP questions.

Quote:

Originally Posted by champrock
What is the value of

1*2 / 3! + (2*2^2)/4! + (3*2^3)/5! ............... (15*2^15)/17!

I tried making a general term for this but was unable to proceed further with that method. Secondly I multiplied the sum by 2 and tried to subtract it from the original (AP-GP sort of a method) but that is also not taking me any further.

Thanks

• Apr 1st 2009, 08:47 PM
champrock
didnt quite get how u are taking 17! as denominator?

and the answer cannot be 1. There is no such option :)
• Apr 1st 2009, 09:06 PM
mr fantastic
Quote:

Originally Posted by Schung
The answer is not quite exactly equal to 1. To paraphrase the greatest spy of all time - Missed it by this much: $\frac{2}{10854718875}$ ....