\(B=\frac{4}{1\times3}+\frac{4}{3\times5}+...+\frac{4}{9\times11}+\frac{4}{11\times13}\)
\(=2\times\left(\frac{2}{1\times3}+\frac{2}{3\times5}+...+\frac{2}{9\times11}+\frac{2}{11\times13}\right)\)
\(=2\times\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}\right)\)
\(=2\times\left(1-\frac{1}{13}\right)\)
\(=2\times\frac{12}{13}\)
\(=\frac{24}{13}\)
B = \(\frac{4}{1.3}+\frac{4}{3.5}+...+\frac{4}{11.13}\)
\(=4\left(\frac{1}{1.3}+\frac{1}{3.5}+...+\frac{1}{11.13}\right)\)
\(=4.\frac{1}{4}.\left(\frac{2}{1}-\frac{2}{3}+\frac{2}{3}-\frac{2}{5}+...+\frac{2}{11}-\frac{2}{13}\right)\)
\(=2-\frac{2}{13}=\frac{24}{13}\)
\(B=\)\(\frac{4}{1.3}\)\(+\)\(\frac{4}{3.5}\)\(+...+\)\(\frac{4}{9.11}\)\(+\)\(\frac{4}{11.13}\)
\(B=\)\(\frac{4}{2}.\)\(\left(\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{9.11}+\frac{2}{11.13}\right)\)
\(B=\)\(2.\)\(\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}\right)\)
\(B=\)\(2.\)\(\left(1-\frac{1}{13}\right)\)\(=\)\(2.\frac{12}{13}\)\(=\)\(\frac{24}{13}\)
#Dấu "." là dấu nhân.
B=\(\frac{4}{1.3}\)+\(\frac{4}{3.5}\)+...+\(\frac{4}{9.11}\)+\(\frac{4}{11.13}\)
B=\(\frac{4}{2}\).\(\frac{2}{1.3}\)+\(\frac{4}{2}\).\(\frac{2}{3.5}\)+...+\(\frac{4}{2}\).\(\frac{2}{9.11}\)+\(\frac{4}{2}\).\(\frac{2}{11.13}\)
B=\(\frac{4}{2}\).(\(\frac{2}{1.3}\)+\(\frac{2}{3.5}\)+...+\(\frac{2}{9.11}\)+\(\frac{2}{11.13}\))
B=2.(\(\frac{1}{1}\)-\(\frac{1}{3}\)+\(\frac{1}{3}\)-\(\frac{1}{5}\)+...+\(\frac{1}{9}\)-\(\frac{1}{11}\)+\(\frac{1}{11}\)-\(\frac{1}{13}\))
B=2.(1-\(\frac{1}{13}\))
B=2.\(\frac{12}{13}\)=\(\frac{24}{13}\)
Chúc bạn học tốt.Nếu buồn thì kb với mình
\(B=\frac{4}{1\times3}+\frac{4}{3\times5}+...+\frac{4}{11\times13}\)
\(B=2\times\left(\frac{2}{1\times3}+\frac{2}{3\times5}+...+\frac{2}{11\times13}\right)\)
\(B=2\times\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{11}-\frac{1}{13}\right)\)
\(B=2\times\left(1-\frac{1}{13}\right)\)
\(B=2\times\frac{12}{13}\)
\(B=\frac{24}{13}\)
~ Hok tốt ~
