Question

Tính tổng A, biết: A = \(1+5^1+5^2+5^3+5^4+...+5^{49}+5^{50}\)

Answer 1

\(5A=5^1+5^2+5^3+...+5^{51}\)

\(4A=5A-A=5^{51}-1\)

\(\Rightarrow A=\frac{5^{51}-1}{4}\)