\(M=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}\)

\(M=\frac{2}{30}+\frac{2}{42}+...+\frac{2}{1980}\)

\(M=2\left(\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{44.45}\right)\)

\(M=2\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{44}-\frac{1}{45}\right)\)

\(M=2\left(\frac{1}{5}-\frac{1}{45}\right)\)

\(M=2\times\frac{8}{45}\)

\(M=\frac{16}{45}\)

\(M=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}\)

\(M=\frac{1\times2}{15\times2}+\frac{1\times2}{21\times2}+\frac{1\times2}{28\times2}+\frac{1\times2}{946\times2}+\frac{1\times2}{990\times2}\)

\(M=\frac{2}{30}+\frac{2}{42}+\frac{2}{56}+...+\frac{2}{1892}+\frac{2}{1980}\)

\(M=2\times\left(\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+...+\frac{1}{1892}+\frac{1}{1980}\right)\)

\(M=2\times\left(\frac{1}{5\times6}+\frac{1}{6\times7}+\frac{1}{7\times8}+...+\frac{1}{43\times44}+\frac{1}{44\times45}\right)\)

\(M=2\times\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{43}-\frac{1}{44}+\frac{1}{44}-\frac{1}{45}\right)\)

\(M=2\times\left(\frac{1}{5}-\frac{1}{45}\right)\)

\(M=2\times\left(\frac{9}{45}-\frac{1}{45}\right)\)

\(M=2\times\frac{8}{45}\)

\(M=\frac{16}{45}\)

Chúc bạn học tốt

\(\frac{M}{2}=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+....+\frac{1}{940}+\frac{1}{990}\)

\(\frac{M}{2}=\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+....+\frac{1}{1892}+\frac{1}{1980}\)

\(\frac{M}{2}=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+......+\frac{1}{43.44}+\frac{1}{44.45}\)

\(\frac{M}{2}=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{43}-\frac{1}{44}+\frac{1}{44}-\frac{1}{45}\)

\(\frac{M}{2}=\frac{1}{5}-\frac{1}{45}=\frac{8}{54}=>M=\frac{8}{45}.2=\frac{16}{45}\)

Vậy M=16/45

\(M=\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}\)

\(\Rightarrow\frac{1}{2}M=\frac{1}{2}\left(\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}\right)\)

\(\Rightarrow\frac{1}{2}M=\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+...+\frac{1}{1892}+\frac{1}{1980}\)

\(\Rightarrow\frac{1}{2}M=\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+...+\frac{1}{43.44}+\frac{1}{44.45}\)

\(\Rightarrow\frac{1}{2}M=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{43}-\frac{1}{44}+\frac{1}{44}-\frac{1}{45}\)

\(\Rightarrow\frac{1}{2}M=\frac{1}{5}-\frac{1}{45}=\frac{9}{45}-\frac{1}{45}=\frac{8}{45}\)

\(\Rightarrow M=\frac{8}{45}:\frac{1}{2}=\frac{8}{45}.2=\frac{16}{45}\)

nhớ ấn đúng cho mình nha

\(M=\frac{2}{30}+\frac{2}{42}+...+\frac{2}{1980}\)

\(=2\left(\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{44.45}\right)\)

\(=2\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{44}-\frac{1}{45}\right)\)

\(=2\left(\frac{1}{5}-\frac{1}{45}\right)\)

\(=2\times\frac{8}{45}\)

\(=\frac{16}{45}\)

\(M=2\left(\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+..+\frac{1}{1980}\right)\)

\(=2\left(\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{44.45}\right)\)

\(=2\left(\frac{1}{5}-\frac{1}{45}\right)\)

\(=\frac{16}{45}\)

Chào bạn, bạn hãy theo dõi bài giải của mình nhé!

\(\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+...+\frac{1}{946}+\frac{1}{990}\)

\(=\frac{2}{30}+\frac{2}{42}+\frac{2}{56}+...+\frac{2}{1892}+\frac{2}{1980}\)

\(=\frac{2}{5\cdot6}+\frac{2}{6\cdot7}+\frac{2}{7\cdot8}+...+\frac{2}{43\cdot44}+\frac{2}{44\cdot45}\)

\(=2\left(\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+...+\frac{1}{43\cdot44}+\frac{1}{44\cdot45}\right)\)

\(=2\left(\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+...+\frac{1}{43}-\frac{1}{44}+\frac{1}{44}-\frac{1}{45}\right)\)

\(=2\left(\frac{1}{5}-\frac{1}{45}\right)=2\left(\frac{9}{45}-\frac{1}{45}\right)=2\cdot\frac{8}{45}=\frac{16}{45}\)

Chúc bạn học tốt!

p=1-1/2.5-1/3.5-1/1.3-1/4.7-1/2.3-1/3.7

p=1-(1/2.1/5-1/3.1/5)-(1/1.1/3-1/2.1/3)-(1/4.1/7-1/3.1/7)

p=1-(1/5.(1/2-1/3))-(1/3.(1-1/2))-(1/7.(1/4-1/3)

p=1-(1/5.1/6)-(1/3.1/2)-(1/7.-1/12)

p=1-1/30-1/6+1/84

p=341/420

=1/4 nha bạn.

P=1-1/3-1/6-1/10-1/15-1/21-1/28

P=2(1/2-1/6-1/12-1/20-1/30-1/42-1/56)

P=2(1/1.2-1/2.3-1/3.4-1/4.5-1/5.6-1/6.7-1/7.8)

P=2(1-1/2-1/2+1/3-1/3+1/4-1/4+1/5-1/5+1/6-1/6+1/7-1/7+1/8)

P=2.1/8

P=1/4

58/380

nó bằng 59/380

tớ cần cách làm bạn ơi

\(S = \frac{1}{3} +\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28} \)

\(S=\frac{1}{3}+\frac{1}{3}.\frac{1}{2}+\frac{1}{5}.\frac{1}{2}+\frac{1}{5}.\frac{1}{3}+\frac{1}{7}.\frac{1}{3}+\frac{1}{7}.\frac{1}{4} \)

\(S=\frac{1}{3}(1+\frac{1}{2})+\frac{1}{5}(\frac{1}{2}+\frac{1}{3})+\frac{1}{7}(\frac{1}{3}+\frac{1}{4})\)

\(S=\frac{1}{3}.\frac{3}{2}+\frac{1}{5}.\frac{5}{6}+\frac{1}{7}.\frac{7}{12}\)

\(S=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}\)

\(S=\frac{6}{12}+\frac{2}{12}+\frac{1}{12}\)

\(S=\frac{9}{12}\)

\(S=\frac{3}{4}\)

S=\(\frac{3}{4}\)

3/4