=1−14 +14 −110 +...+119 −122
=1−122
= \(\frac{21}{22}\)
k cho mình nha chắc chắn đúng 100 %
\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{10}+...+\frac{1}{19}-\frac{1}{22}\)
\(=1-\frac{1}{22}\)
\(=\frac{21}{22}\)
\(=\frac{1}{3}\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{16.19}+\frac{3}{19.22}\right)\)
\(=\frac{1}{3}\left(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+...+\frac{1}{19}-\frac{1}{20}\right)\)
\(=\frac{1}{3}\left(1-\frac{1}{20}\right)\)
\(=\frac{1}{3}.\frac{19}{20}\)
\(=\frac{19}{60}\)
