\(\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{19.21}-x+\frac{221}{231}=\frac{4}{3}\)
\(=2\left(\frac{1}{11.13}+\frac{1}{13.15}+...+\frac{1}{19.21}\right)-x+\frac{221}{231}=\frac{4}{3}\)
\(=2.\frac{1}{2}\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right)-x+\frac{221}{231}=\frac{4}{3}\)
\(=\left(\frac{1}{11}-\frac{1}{21}\right)-x+\frac{221}{231}=\frac{4}{3}\)
\(=\frac{10}{231}-x+\frac{221}{231}=\frac{4}{3}\)
\(\frac{10}{231}-x=\frac{4}{3}-\frac{221}{231}\)
\(\frac{10}{231}-x=\frac{29}{77}\)
\(x=\frac{10}{231}-\frac{29}{77}\)
\(x=\frac{-1}{3}\)
có cần cầu kì vậy ko bn, còn cách nào dễ hỉu hơn ko
