c; (\(\dfrac{9}{2}\) - 2\(x\)) . \(\dfrac{11}{7}\) = \(\dfrac{11}{14}\)

    \(\dfrac{9}{2}\) - 2\(x\)           = \(\dfrac{11}{14}\) : \(\dfrac{11}{7}\)

     \(\dfrac{9}{2}\) - 2\(x\)          = \(\dfrac{1}{2}\)

           2\(x\)           = \(\dfrac{9}{2}-\dfrac{1}{2}\)

           2\(x\)          = 4

           \(x\)           = 4 : 2

            \(x\)          = 2 

Vậy \(x\)         = 2 

Câu 10 a; \(\dfrac{11}{7}\) + \(\dfrac{-5}{3}\) = \(\dfrac{33}{21}\) + \(\dfrac{-35}{21}\) = \(\dfrac{-2}{21}\)

             b; \(\dfrac{-4}{7}\) + \(\dfrac{2}{3}\). \(\dfrac{-9}{14}\) = \(\dfrac{-4}{7}\) + \(\dfrac{-3}{7}\) = -1

                  c; \(\dfrac{-5}{12}\).\(\dfrac{2}{11}\) + \(\dfrac{-5}{12}\).\(\dfrac{9}{11}\) + \(\dfrac{5}{12}\)

                    = \(\dfrac{-5}{12}\) x (\(\dfrac{2}{11}\) + \(\dfrac{9}{11}\) - 1)

                    = - \(\dfrac{5}{12}\) x 0

                   = 0 

Lời giải:

$A=\frac{3}{5}\left(\frac{5}{9.14}+\frac{5}{14.19}+\frac{5}{19.24}+...+\frac{5}{(5n-1)(5n+4)}\right)$

$\frac{3}{5}\left(\frac{14-9}{9.14}+\frac{19-14}{14.19}+\frac{24-19}{19.24}+...+\frac{(5n+4)-(5n-1)}{(5n-1)(5n+4)}\right)$

$=\frac{3}{5}\left(\frac{1}{9}-\frac{1}{14}+\frac{1}{14}-\frac{1}{19}+\frac{1}{19}-\frac{1}{24}+...+\frac{1}{5n-1}-\frac{1}{5n+4}\right)$

$=\frac{3}{5}(\frac{1}{9}-\frac{1}{5n+4})$

$=\frac{1}{15}-\frac{3}{5(5n+4)}< \frac{1}{15}$

ko càn giải bài này nha

1. Does your room have a colorful picture
2. Nobody in his class is better at English than Peter
3. Why don't we have a picnic in the park on the weekend
4. My house is not far from the supermarket
5. What is the price of these red notebooks
6. Many people go to work by walking for their health
7, How many hours do you spend watching television
8. Shall we go to the cinema tonight
9. The novel was much more interesting than the film
10. He seemed like a friendly person, but I didn't like him

1. Is there a colorful picture in your room ?

   Does ………your room have a colorful picture……………………………………………………………….?

2. Peter is best at English in his class.

   Nobody …in Peter's class is as good at English as him………………………………………………………………?

3. Let’s have a picnic in the park on the weekend.

   Why …don't we have a picnic in the park on the weekend……………………………………………………………………..?

4. My house is near the supermarket .

   My house is not ……far from the supermerket……………………………………………………?

5. How much are these red notebooks .

   What ……is the price of these red notebooks…………………………………………………………………..?

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