How do you find the sum of the first 10 terms of $1+9+81+729+...$ ?

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Answer 1 · 2016-07-26T09:29:21

$435,848,050$

First we need to know whether it is an AP or GP.??

The difference changes, so it is not an AP. However $81/9 =9/1 = 9$
So it is a GP.

$a = 1 and r = 9$

Use the formula for the sum of $n$ terms:

$S_n = (a(r^n - 1))/(r-1)$

For n = 10.

$S_n =(1(9^10 -1))/(9-1)$

This is the huge answer of $435,848,050$

How do you find the sum of the first 10 terms of 1+9+81+729+...1+9+81+729+...?