\(D=\left(1-\frac{1}{2}\right)+\left(1-\frac{1}{6}\right)+\left(1-\frac{1}{12}\right)+\left(1-\frac{1}{20}\right)\)
\(=\left(1+1+1+1\right)-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}\right)\)
\(=4-\left(\frac{2-1}{1.2}+\frac{3-2}{2.3}+\frac{4-3}{3.4}+\frac{5-4}{4.5}\right)\)
\(=4-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}\right)\)
\(=4-\left(1-\frac{1}{5}\right)=4-\frac{4}{5}=\frac{16}{5}\)
\(D=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}\)
\(D=\left(1+1+1+1\right)-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}\right)\)
\(D=4-\frac{4}{5}\)
\(D=\frac{16}{5}\)
D=\(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}\)= \(\left(\frac{1}{2}+\frac{19}{20}\right)+\left(\frac{5}{6}+\frac{11}{12}\right)\)=\(\left(\frac{10}{20}+\frac{19}{20}\right)+\left(\frac{10}{12}+\frac{11}{12}\right)\)
= \(\frac{29}{20}+\frac{7}{4}\)=\(\frac{29}{20}+\frac{35}{20}=\frac{64}{20}=\frac{16}{5}\)
\(D=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}\)
\(\Rightarrow\)\(D=\left(1+1+1+1\right)-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}\right)\)
\(\Rightarrow D=4-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}\right)\)
\(\Rightarrow D=4-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{4}-\frac{1}{5}\right)\)
\(\Rightarrow D=4-\left(1-\frac{1}{5}\right)\)\(\Rightarrow D=4-\frac{4}{5}\)\(\Rightarrow D=\frac{16}{5}\)
D= 1+1+1+1-\(\frac{1}{2}-\frac{1}{6}-\frac{1}{12}-\frac{1}{20}\)
D=4+\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}\)
D=4+\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}\)
D=5-\(\frac{1}{5}\)=\(\frac{24}{5}\)
Ở trên mk lm nhầm dấu nha bn !
Sửa lại nè ;
D=4-\(\frac{1}{2}-\frac{1}{6}-\frac{1}{12}-\frac{1}{20}\)
D=4-\(1+\frac{1}{2}-\frac{1}{2}+\frac{1}{3}-\frac{1}{3}+\frac{1}{4}-\frac{1}{4}+\frac{1}{5}\)
D=\(3+\frac{1}{5}\)=\(\frac{16}{5}\)
