\(E=\frac{5}{2\cdot4}+\frac{5}{4\cdot6}+...+\frac{5}{98\cdot100}\)
\(2E=\frac{5}{2}-\frac{5}{4}+\frac{5}{4}-\frac{5}{6}+...+\frac{5}{98}-\frac{5}{100}\)
\(2E=\frac{5}{2}-\frac{1}{20}\)
\(2E=\frac{49}{20}\)
\(E=\frac{49}{20}\cdot\frac{1}{2}=\frac{49}{40}\)
Đặt \(E=\frac{5}{2.4}+\frac{5}{4.6}+...+\frac{5}{98.100}\)
\(=1-\left(\frac{5}{2}-\frac{5}{4}\right)+\left(\frac{5}{4}-\frac{5}{6}\right)+...+\left(\frac{5}{98}-\frac{5}{100}\right)\)
\(=1-\frac{5}{100}\)
\(=\frac{95}{100}\)
\(E=\frac{5}{2.4}+\frac{5}{4.6}+...+\frac{5}{98.100}\)
\(\Leftrightarrow E=\frac{5}{2}\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+...+\frac{1}{98}-\frac{1}{100}\right)\)
\(\Leftrightarrow E=\frac{5}{2}\left(\frac{1}{2}-\frac{1}{100}\right)\)
\(\Leftrightarrow E=\frac{5}{2}\cdot\frac{49}{100}\)
\(\Leftrightarrow E=\frac{49}{40}\)
\(\frac{49}{20}\)nhé!
Cho mình 1 k nhé!
THANK YOU!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
\(E=5\left(\frac{1}{2\cdot4}+\frac{1}{4\cdot6}+...+\frac{1}{98\cdot100}\right)\)
\(E=5\cdot\left[\frac{1}{2}\left(\frac{1}{2}-\frac{1}{4}\right)+\frac{1}{2}\left(\frac{1}{4}-\frac{1}{6}\right)+...+\frac{1}{2}\left(\frac{1}{98}-\frac{1}{100}\right)\right]\)
\(E=5\cdot\frac{1}{2}\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+...+\frac{1}{98}-\frac{1}{100}\right)\)
\(E=\frac{5}{2}\cdot\left(\frac{1}{2}-\frac{1}{100}\right)\)
\(E=\frac{5}{2}\cdot\frac{49}{100}\)
\(E=\frac{49}{40}\)
E =5/2.4 + 5/4.6 +.......+5/98.100
E:5=1/2.4+1/4.6+..........+1/98.100
E:5=1/2-1/4+1/4-1/6 + ........+1/98-1/100
E:5=1/2-1/100=49/100
E=49/100 x 5 =49/20
ban tu biet nha ban
3/7 nhé bn nhớ k mk nhé
