Problem 646

Find S11 for 1 + 2 + 4 + 8 + …

Solution:-

Sn =

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r^{n} $)}{(1 - r)}$ , Where a1 = first term , r = common ratio and n = finding term.

a1 = 1 , r = 2 , n = 11

S11 = $\frac{1(1 - 2^{11})}{(1-2)}$

S11 = 2047

So the value of S11 2047