Để mình làm lại nguyên bài cho dễ hiểu nhé
\(A=\frac{2}{60.63}+\frac{2}{63.66}+\frac{2}{66.69}+..+\frac{2}{117.120}+\frac{2}{2011}\)
\(=\frac{2}{3}\left(\frac{2}{60}-\frac{2}{63}+\frac{2}{63}-\frac{2}{66}+\frac{2}{66}-\frac{2}{69}+...+\frac{2}{117}-\frac{2}{120}\right)+\frac{2}{2011}\)
\(=\frac{2}{3}\left(\frac{2}{60}-\frac{2}{120}\right)+\frac{2}{2011}=\frac{2}{3}.\frac{1}{60}+\frac{2}{2011}=\frac{4382}{361980}\)
Sorry nhé! nãy giờ nhìn không kĩ đề
\(A=\frac{2}{60.63}+\frac{2}{63.66}+\frac{2}{66.69}+...+\frac{2}{117.120}\)
\(=\frac{2}{3}\left(\frac{2}{60}-\frac{2}{63}+\frac{2}{63}-\frac{2}{66}+\frac{2}{66}-\frac{2}{69}+...+\frac{2}{117}-\frac{2}{120}\right)\)
\(=\frac{2}{3}\left(\frac{2}{60}-\frac{2}{120}\right)=\frac{2}{3}.\frac{1}{60}=\frac{2}{180}\)
Suy ra \(A=\frac{2}{180}\)
\(A=\frac{2}{60\cdot63}+\frac{2}{63\cdot66}+...+\frac{2}{117\cdot120}+\frac{2}{2011}\)
\(=\frac{2}{60}-\frac{2}{63}+\frac{2}{63}-\frac{2}{66}+...+\frac{2}{117}-\frac{2}{120}+\frac{2}{2011}\)
\(=\frac{2}{60}-\frac{2}{120}+\frac{2}{2011}\)
\(=\frac{2071}{120660}\)
Cho mình bổ sung thêm nhé: \(=\frac{2}{3}.\frac{1}{60}+\frac{2}{2011}=\frac{2}{180}+\frac{2}{2011}=\frac{4022}{361980}+\frac{360}{361980}=\frac{4382}{361980}\)
Suy ra \(A=\frac{4382}{361980}\)
Mình thiếu nhé bạn
