1 C

2 C

3 C

4 C

5 A

6 B

7 A

11 

12 B

13 A

14 C

15D

4. B

5. A

6. C

7. C

8. B

9. B

10. A

11. C

12. 

13. A

14. 

15. C

1D

2B

3B

4B

5C

6A

7A

8C

bh ròi bn còn cần giúp nx ko?

A = \(\dfrac{x+13}{x+2}\)  (đk \(x\) ≠ -2)

Em cần làm gì với biểu thức này?

\(\frac{4-5}{7}=\frac{-1}{7}\)

\(4-\frac{5}{7}\)

\(=\frac{4}{1}-\frac{5}{7}\)

\(=\frac{28-5}{7}\)

\(=\frac{23}{7}\)

Chuẩn 100%

23 phan 7 k nha

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P/s: Mình nghĩ nói ngắn quá sẽ không có điểm cao lắm đâu, không cần nói quá dài hoặc quá ngắn. Chỉ cần đầy đủ ý trong bài là ok. Với lại khi nói bạn nhớ phải tự tin lên nha. FIGHTING!!!!

p: \(\dfrac{5}{1\cdot2}+\dfrac{5}{2\cdot3}+...+\dfrac{5}{50\cdot51}\)

\(=5\left(\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+...+\dfrac{1}{50\cdot51}\right)\)

\(=5\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{50}-\dfrac{1}{51}\right)\)

\(=5\cdot\left(1-\dfrac{1}{51}\right)=5\cdot\dfrac{50}{51}=\dfrac{250}{51}\)

q: \(\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{10}+...+\dfrac{1}{210}\)

\(=\dfrac{2}{6}+\dfrac{2}{12}+\dfrac{2}{20}+...+\dfrac{2}{420}\)

\(=2\left(\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+...+\dfrac{1}{420}\right)\)

\(=2\left(\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{20\cdot21}\right)\)

\(=2\left(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{20}-\dfrac{1}{21}\right)\)

\(=2\left(\dfrac{1}{2}-\dfrac{1}{21}\right)=2\cdot\dfrac{19}{42}=\dfrac{19}{21}\)

2/3 x 4/5 x 25 = 8/15 x 25 = 40/3