Question

[Trần Hà Tiên]

\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+...+\frac{2}{x\left(x-1\right)}=\frac{2007}{2009}\)

Answer 1

[Trần Đức Thắng]

\(\frac{1}{2.3}=\frac{1}{2}-\frac{1}{3}\) trong đó 3 = x ; 2 = x - 1 

\(\frac{1}{\left(x-1\right)x}=\frac{1}{x-1}-\frac{1}{x}\)