Question

Tính tổng

S = 5 + 5^2 + 5^3 + 5^4+....+ 5^2006

Tặng 2 tick cho ai nhanh nhất nhé

Answer 1

5S-S=(5^2+5^3+5^4+...+5^2007)-(5+5^2+5^3+...+5^2006)

4S=5^2007-5

S=(5^2007-5):4

Answer 2

\(S=5+5^2+5^3+5^4+...+5^{2006}\)

\(5S=5^2+5^3+5^4+5^5+...+5^{2007}\)

\(5S-S=\left(5^2+5^3+5^4+5^5+...+5^{2007}\right)-\left(5+5^2+5^3+5^4+...5^{2006}\right)\)

\(4S=5^{2007}-5\)

\(\Rightarrow S=\frac{5^{2007}-5}{4}\)