\(S=\dfrac{2}{1\cdot4}+\dfrac{2}{4\cdot7}+\dfrac{2}{7\cdot10}+\dfrac{2}{10\cdot13}+\dfrac{2}{13\cdot16}+\dfrac{2}{16\cdot19}+\dfrac{2}{19\cdot22}\)
\(S=\dfrac{2\cdot1}{1\cdot4}+\dfrac{2\cdot1}{4\cdot7}+\dfrac{2\cdot1}{7\cdot10}+\dfrac{2\cdot1}{10\cdot13}+\dfrac{2\cdot1}{13\cdot16}+\dfrac{2\cdot1}{16\cdot19}+\dfrac{2\cdot1}{19\cdot22}\)
\(S=2\cdot\left(\dfrac{1}{1\cdot4}+\dfrac{1}{4\cdot7}+\dfrac{1}{7\cdot10}+\dfrac{1}{10\cdot13}+\dfrac{1}{13\cdot16}+\dfrac{1}{16\cdot19}+\dfrac{1}{19\cdot22}\right)\)
\(S=2\cdot\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{16}+\dfrac{1}{16}-\dfrac{1}{19}+\dfrac{1}{19}-\dfrac{1}{22}\right)\)
\(S=2\cdot\left(1-\dfrac{1}{22}\right)\)
\(S=2\cdot\dfrac{21}{22}\)
\(S=\dfrac{42}{22}\)
\(S=\dfrac{21}{11}\)
Giúp Mình Gải chi tiết đc ko ? Mình cần gấp
