Question

1+1/3+1/9+1/27+1/81+1/243+1/729 = ?

Answer 1

\(M=1+\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+\frac{1}{3^4}+\frac{1}{3^5}+\frac{1}{3^6}\)

\(\Rightarrow3M=3+1+\frac{1}{3^2}+\frac{1}{3^3}+\frac{1}{3^4}+\frac{1}{3^5}\Rightarrow3M-M=3-\frac{1}{3^6}\Rightarrow2M=\frac{2186}{729}\)

\(\Rightarrow M=\frac{1093}{729}\).Nhớ LIKE nha