\(=\frac{1}{\frac{2.\left(1+2\right)}{2}}+\frac{1}{\frac{3.\left(3+1\right)}{2}}=\frac{1}{\frac{4.\left(4+1\right)}{2}}+...+\frac{1}{\frac{99.\left(99+1\right)}{2}}+\frac{1}{50}\)
\(=\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+...+\frac{2}{99.100}+\frac{1}{50}\)
\(=2.\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{99.100}\right)+\frac{1}{50}\)
\(=2.\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{99}-\frac{1}{100}\right)+\frac{1}{50}\)
\(=2.\frac{49}{100}+\frac{1}{50}\)
\(=\frac{49}{50}+\frac{1}{50}\)
\(=1\)
=1 (violympic vong 10 dung to da lam roi)
