Tìm các cặp số nguyên âm (a,b) sao cho: \(\dfrac{a}{4}\)-\(\dfrac{1}{2}\)=\(\dfrac{3}{b}\)

1. Tìm 2 số hữu tỉ a,b biết:

a - b = 2 (a + b) = a : b

2. Cho các số a, b, c, x, y, z

\(\dfrac{x}{a}\)=\(\dfrac{y}{b}\) =\(\dfrac{z}{c}\)Chứng minh rằng: \(\dfrac{bz-cy}{a}\)= \(\dfrac{cx-az}{y}\)=\(\dfrac{ay-bx}{c}\)

3. Tìm các cặp số nguyên âm (a,b) sao cho: \(\dfrac{a}{4}\) -\(\dfrac{1}{2}\)=\(\dfrac{3}{b}\)

Điền giới từ thích hợp:

1. He said the train would be leaving the station ............. 25 minutes.

2. My father met my mother ......... the war

3. Those men have been working on the motor ........... three hours now

4. The students have been here ......... the begining ......... the semester

5. She said she was going to returned to Nha Trang ....... the tenth of August

6. The train will leave the Hang Co Station ....... twelve minutes

7. Wait right here for me. I'll be away ...... 15 minutes.

8. Our boss, Mr. Thanh, has worked for thí company ........ the war

9. My sister and I make trips to nearby cities ....... time ...... time

10. Once ........... a while, I enjoy eating at a Chinese restaurant

11. Hoang's command of English is improving day .... day

12. I don't think Mr Thanh plans to stay in HN ......... very long

13. My father called to tell me to go home ........ once

14. We got there just ....... time to see the end of the program

15. We had taken a taxi in order to get to the meeting ......... time

1. Write about your hobby (play badminton, reading and listening to music)

2. Write a paragraph about how to learn English

3. Write paragraphs about school activities

Mọi người giúp mình với nha!

A thief (steal) ____ my money. Fortunately, the police (catch) ____ the thief a little while later. Later I (fall) ____ in some slipper steps (hurt) ___ my arms. Then a little boy (throw) ___ a ball (hit) ____ me accidentally. After that, I ___ down again and ___ my new watch (fall/ down/ break)

Chứng minh rằng:

\(\frac{1}{3}\)+ \(\frac{1}{3^2}\)+\(\frac{1}{3^3}\)+ .... + \(\frac{1}{3^{99}}\)< \(\frac{1}{2}\)

Đặc điểm quang học của thấu kính phân kì là gì?

Cho tam giác ABC vuông tại A có AB = 6cm, BC = 10cm. Kẻ một đường thẳng song song với BC, cắt các cạnh AB và AC tại E và F. Biết AE = 2cm, tính tỉ số đồng dạng của Δ A E F , Δ A B C  và độ dài các đoạn cạnh AF, EF