Question

Tính hợp lý : 

M= \(\dfrac{15}{7.8}\) - \(\dfrac{17}{8.9}\) + \(\dfrac{1}{9.10}\) + \(\dfrac{1}{10.11}\)

Answer 1

\(M=\dfrac{15}{7\cdot8}-\dfrac{17}{8\cdot9}+\dfrac{1}{9\cdot10}+\dfrac{1}{10\cdot11}\)

\(M=\dfrac{1}{8}+\dfrac{1}{7}-\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{11}\)

\(M=\dfrac{1}{7}-\dfrac{1}{11}=\dfrac{11-7}{7\cdot11}=\dfrac{4}{77}\)

Answer 2

`M=15/(7.8)-17/(8.9)+1/(9.10)+1/(10.11)`

`=1/7-1/8-(1/8-1/9)+1/9-1/10+1/10-1/11`

`=1/7-1/4+2/9-1/11`

`=67/2772`

Theo mình đề bài sai phải là `M=15/(7.8)-17/(8.9)+1/(9.10)+1/(10.11)`

`=1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11`

`=1/7-1/11=4/77`

Answer 3

M=18+17−18−19+19−110+110−111M=18+17−18−19+19−110+110−111

Answer 4

Giải:

\(M=\dfrac{15}{7.8}-\dfrac{17}{8.9}+\dfrac{1}{9.10}+\dfrac{1}{10.11}\) 

\(M=\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{11}\) 

\(M=\dfrac{1}{7}-\dfrac{1}{11}\) 

\(M=\dfrac{4}{77}\)