Tìm n :

A = \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+.....+\frac{1}{n}\)

Biết A = \(\frac{39}{40}\)

Cho A = \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{n}\)

Biết A = \(\frac{39}{40}\). Tìm n

Cho \(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{n}\)

Biết \(A=\frac{39}{40}\)Tìm n

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{n}\)

biết A=\(\frac{39}{40}\)

tìm n

Cho M = \(\frac{1}{2}\)+   \(\frac{1}{6}\)+  \(\frac{1}{12}\)+  \(\frac{1}{20}\)+  \(\frac{1}{30}\)+   ...   +  \(\frac{1}{n}\)

Tìm n biết M =\(\frac{39}{40}\)