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191) What would be the formuls

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191) What would be the formuls

by ern5231 » Thu May 13, 2010 11:57 pm
The series 1 +2 +2 ^ 2 +2 ^ 3 + ... ... 2 ^ n can be represented by which formula?(given N=9)
a) (10 ^ 5 +1) (10 ^ 5-1)
b) (10 ^ 5-1) (10 ^ 5-1)

I recollect this question from a mock test at my prep center. I am sorry I don't recollect further option. how do we approach such problems?Do we use GP here?
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by mj78ind » Fri May 14, 2010 12:16 am
I think GP looks like the way to go .... Sum of n terms of GP, with a as 1st term r as ratio = a(r^n-1)/(r-1), which in this case should translate into:

2^0 (2^9-1)/(2-1) = 2^9-1
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