Question

$a = 1 + 3 + {3}^{2} + {3}^{3} ...... + {3}^{2015}$
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Answer 1

Explicație pas cu pas:

a=1+3+3²+....+3²⁰¹⁵/*3 =>

3a=3+3²+....+3²⁰¹⁵+3²⁰¹⁶

=> 3a-a=3+3²+...+3²⁰¹⁵+3²⁰¹⁶-1-3-3²-...-3²⁰¹⁵ =>

2a=3²⁰¹⁶-1=>a=(3²⁰¹⁶-1)/2