Đa giác n - cạnh có số đường chéo là 170
Ta có :
`(n(n-3))/2=170`
`⇔n^2-3n=340`
`⇔n^2-3n-340=0`
`⇔(n-20)(n+17)=0`
vì` n>0`
`⇒n-20=0`
`⇒n=20`
Ta có : `\frac{n(n-3)}{2}=170`
`n^{2}-3n=170.2`
`n^{2}-3n=340`
`n^{2}-3n-340=0`
Vì `n>0`
`=>n=20`
I. Choose A, B, C or D to indicate the correct answer to each of the following questions. 1.How do you start the computer? A. How does the computer turn on? B. How do you turn on the computer? C. How do you turn the computer on? D. Both B and C are correct 2. Please ________ the light, it’s getting dark here. A. turn on B. turn off C. turn over D. turn into 3. Shall we go somewhere _______ a drink? A. for B. from C. to D. of 4. It's very cold in here. Do you mind if I turn ________ the heating? A. down B. away C. off D. on 5. Mike ________ Alaska, so he's used to cold weather. A. comes over B. comes in C. comes across D. comes from 6. Jane had a difficult childhood. She _______ a broken home. A. came from B. came over C. came in D. came up with 7. My father gave up smoking two years ago. A. liked B. continued C. stopped D. enjoyed 8. She ______ a new hat. A. have on B. has on C. have to D. has to 9. I always ______ my socks on first. A. put B. lie C. leave D. lay 10. Did you ______ it on before you bought it? A. watch B. see C. test D. try 11. Please take ______ your coat. A. on B. off C. over D. up 12. I dusted ______ the bookshelf. Phủi bụi A. off B. on C. out D. over 13. We need to ______ this closet. A. clean out B. put on C. cross out D. move away 14. Could you turn the TV ______? A. up B. down C. above D. off 15. Peter ______ his hometown in order to star his business. A. came back B. came up with C. came over D. came off 16. I usually ______ at 6 a.m every day. A. get over b phục B. get out of C. wake over D. get up 17. He ______ in this countryside. A. grew up B. grew over C. grew down D. grew out 18. Don’t ______ late. It’s not good for your health. A. stay away from B. stay out C. stay up D. stay along 19. The teacher asked her students to ______. A. sit on B. sit off C. sit up D. sit down 20. I’m standing ______ in the front of the CGV cinema. Can you pick me up? A. on B. off C. down D. up 21. Lisa helped Rose ______ the dishes. A. and B. with C. without D. between 22. Do you often ______ Chinese music in your free time? A. hear to B. listen to C. see to D. have to 23. ______ page 52 in this textbook, you will understand thing I have just talked. A. Look up B. Look down to C. Look at D. Look on 24. Where are you? I have been ______ for hours. A. hearing B. waiting C. standing D. sitting 25. I always ______ problems that I haven’t solved. A. think to B. think about C. think with D. think on
Calli chữ "Ngủ ngon :33" Y/C: - Tone cyan. - Đổ bóng/trang trí cackieu. - Có tâm giúp ạ :33 ~~Hóng~~
Read the passage, then do the tasks. ROBOTS A robot is a machine. But it is not just any machine. It is a special kind of machine. It is a machine that moves. It follows instructions. The instructions come from a computer. Because it is a machine, it does not make mistakes. And it does not get tired. And it never complains. Unless you tell it to! Robots are all around us. Some robots are used to make things. For example, robots can help make cars. Some robots are used to explore dangerous places. For example, robots can help explore volcanoes. Some robots are used to clean things. These robots can help vacuum your house. Some robots can even recognize words. They can be used to help answer telephone calls. Some robots look like humans. But most robots do not. Most robots just look like machines. Long ago, people imagined robots. But nobody was able to make a real robot. The gist real robot was made in 1961. It was called Unimate. It was used to help make cars. It looked like a giant arm. In the future, we will have even more robots. They will do things that we can’t do. Or they will do things that we don’t want to do. Or they will do things that are too dangerous for us. They will help make life better. Answer the questions. 1. What is a robot? 2. Why doesn’t a robot make mistakes? 3. Do most robots look like humans? 4. When was the first robot made? 5. What did the first robot look like? 6. Will robots make our lives better or worse?
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Tính cộng trừ hữu tỉ: Giúp em với ạ
Tìm GTNN : `A={x+3}/{\sqrt[x]+1}` với `x≥0`
Phân tích các đa thức sau thành nhân tử : cả 4 phần ạ!
Viết tập hợp D các tháng trong quý 4
Làm nhanh, chính xác = ctrlhn và 5 sao
($\frac{1}{2}$ - $\frac{7}{13}$ - $\frac{1}{3}$) + ($\frac{-6}{13}$ + $\frac{1}{2}$ + $\frac{4}{3}$)
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