Question

S=1+3+3²+......+3¹⁰⁰. Hãy tính tổng ?

Answer 1

Ta có: S=1+3+3²+......+3¹⁰⁰

=> 3S=3+3²+......+3¹⁰⁰+3¹⁰¹

=> 3S-S=(3+3²+......+3¹⁰⁰+3¹⁰¹)-(1+3+3²+......+3¹⁰⁰)

=> 2S=3¹⁰¹-1

=> \(S=\frac{3^{101}-1}{2}\)

Answer 2

=> 3S = 3+3²+3³+...+3¹⁰¹

=>3S-S=2S=(3+3²+...+3¹⁰¹)-(1+3+...+3¹⁰⁰)=3¹⁰¹-1