Question

 

   6            6                        6

------- + --------- + .... + ------------ 6×7       7×8                 49×50

Answer 1

Đề là ntn hả  cậu ?

`6/6.7 + 6/7.8 + .... + 6/49.50`

Answer 2

\(\dfrac{6}{6\cdot7}+\dfrac{6}{7\cdot8}+...+\dfrac{6}{49\cdot50}\)
\(=6\left(\dfrac{1}{6\cdot7}+\dfrac{1}{7\cdot8}+...+\dfrac{1}{49\cdot50}\right)\)
\(=6\left(\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+...+\dfrac{1}{49}-\dfrac{1}{50}\right)\)
\(=6\left(\dfrac{1}{6}-\dfrac{1}{50}\right)\)
\(=6\cdot\dfrac{1}{6}-6\cdot\dfrac{1}{50}\)
\(=1-\dfrac{3}{25}\)
\(=\dfrac{25}{25}-\dfrac{3}{25}=\dfrac{22}{25}\)