Question

Tính A bt: A=1/3+1/3^2+1/3^3+. . . +1/3^8 Giúp mik vs nhé mik đang cần gấp cảm ơn nhiều hok tốt!

Answer 1

\(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^8}\)

\(3A=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^7}\)

\(3A-A=\left(1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^7}\right)-\left(\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^8}\right)\)

\(2A=1-\frac{1}{3^8}\)

\(A=\frac{1}{2}-\frac{1}{2.3^8}\)