Ta có: \(\frac{1}{2}+\frac{1}{-3}+\frac{1}{4}+\frac{1}{6}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{6}+\frac{1}{4}\)

\(=\frac{1}{6}+\frac{1}{6}-\frac{1}{4}\)

\(=\frac{1}{3}+\frac{1}{4}=\frac{7}{12}\)

1phan2+ 1phan4 < 1

1phan 5+ 2 phan 13 < 1

 1phan 12+ 2 phan 14 < 1

1phan 2 +2phan 3 > 1

e

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\)

=\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\)

=\(\frac{2-1}{1.2}+\frac{3-2}{2.3}+\frac{4-3}{3.4}+\frac{5-4}{4.5}+\frac{6-5}{5.6}+\frac{7-6}{6.7}+\frac{8-7}{7.8}+\frac{9-8}{8.9}\)

=\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\)

=\(1-\frac{1}{9}=\frac{8}{9}\)

1/2 + 1/6 + 1/12 + ... + 1/72

= 1/1.2 + 1/2.3 + 1/3.4 + ... + 1/8.9

= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/8 - 1/9

= 1 - 1/9

= 8/9

ban dan nhanh nhất

ban dan là gì vậy

Chính là ban dan.