:V toán lp 3 cơ ak
A = \(\frac{1}{2}+\frac{1}{6}+\frac{1}{18}+...+\frac{1}{4347}\)
\(A\cdot3=\frac{3}{2}+\frac{1}{2}+\frac{1}{6}+...+\frac{1}{1449}\)
\(A\cdot3-A=\left(\frac{3}{2}+\frac{1}{2}+\frac{1}{6}+...+\frac{1}{1449}\right)-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{18}+...+\frac{1}{4347}\right)\)
\(A\cdot2=\frac{3}{2}+\frac{1}{2}+\frac{1}{6}+...+\frac{1}{1449}-\frac{1}{2}-\frac{1}{6}-\frac{1}{18}-...-\frac{1}{4347}\)
\(A\cdot2=\frac{3}{2}-\frac{1}{4347}\)
\(A\cdot2=\frac{13039}{8694}\)
\(A=\frac{13039}{8694}:2\)
\(A=\frac{13039}{17388}\)
Kết quả hơi lớn nên kiểm tra lại đề :))
