a) Cho 13 số hữu tỉ, trong đó tổng của 4 số bất kì nào cũng là một số dương. Hỏi tổng của 13 số đó là số dương hay số âm. b) Cho . Chứng minh: c) Cho a + b + c = a2 + b2 + c2 = 1 và

làm giúp mình chính xác, chi tiết câu này mình sẽ vote 5 sao, cho câu trả lời hay nhất làm sai, làm bừa, làm thiếu mình sẽ kiện thực hiện phép tính ( hợp lí nếu có thể ): a) -220- ( - 120 ) + ( + 130 ) + 70 b) 13 . ( 47 - 25 ) - 47 . ( 13 - 25 ) c) ( 1597 - 339 ) + ( - 1597 + 639 ) d) - ( -526 ) + ( - 350 ) + ( -150 ) + 74

II. Complete the second sentence in each pair so that it has similar meaning to the first sentence. 1. If you cook the vegetables too long, the vitamins in it will be destroyed. → Cooking__________________________________________________________ 2. They are preparing your food right now. → Your_____________________________________________________________ 3. Follow these safety instructions or you may get burnt. → If you____________________________________________________________ 4. I suggest having spaghetti and pizza tonight. → Let’s_____________________________________________________________ 5. My aunt has never tasted sushi before. → This is____________________________________________________________ 6. You need to peel the onion and slice it. → The onion_________________________________________________________ 7. Eating healthy foods is very important. → It is______________________________________________________________ 8. The rice must be cleaned before cooking. → You______________________________________________________________ 9. They think the café will be busy all year. → The______________________________________________________________ 10. It’s necessary to order the paella in advance. → The paella_____________________________________________________ III. Use the given words to write the complete sentences. 1. There/ nothing more appetizing/ smell of meat sizzling over an open fire. _________________________________________________________________ 2. Some people/ eat barbecue/ because/ it/ let/ together with friends or family/make/ feel more sociable. _________________________________________________________________ 3. People often/ barbecue/ national holidays/ special occasions/ birthday/ family gathering. _________________________________________________________________ 4. In the United States, it/ tradition/ have a barbecue/ hamburgers and hot dogs/ Independence Day, July 4th. _________________________________________________________________ 5. If you/ chance to visit/ different places/ world, you/ try/ local specialities. _________________________________________________________________ 6. There/ any good restaurants/ that town/ we/ decide/ take/ sandwiches for the trip. _________________________________________________________________ 7. We'd like/ stay longer/ try local dishes, but we/ not have/ time. _________________________________________________________________ 8. He/ learn to become/ good cook/ big restaurants and hotels/ if/ he/ try/ hard. _________________________________________________________________ 9. We/ have/ fish? This restaurant/ most famous for it/ this town. _________________________________________________________________ 10. If she/ like/ eat spicy food/ she/ add chilli. _________________________________________________________________ IV. Finish each of the following sentences so that its meaning stays the same. 1. Follow these safety instructions or you may get burnt. → If you ____________________________________________________________ 2. I suggest having some spaghetti and pizza tonight. →Why don't ______________________________________________________ 3. My aunt has never tasted sushi before. → This is ________________________________________________________ 4. Eating healthy food is very important. → It is __________________________________________________________ 5. Do more exercise or you can't lose any weight. → If ____________________________________________________________ 6. Although Jimmy was stronger of the two, his attacker soon overpowered him. → Despite his ________________________________________________________ 7. I don't intend to change my eating habits. →I have _____________________________________________________________ 8. If I follow the doctor's advice of eating diet, I can improve my health problems soon. → The sooner ________________________________________________________ 9. You need to peel the onion and slice it. →The onion __________________________________________________________ 10. The manager usually threatens not to select Brian for the team unless he trains harder. → If _________________________________________________________________

Mình ko hiểu bài này giúp mình mai mình phải nộp r ạ

Vẽ boy cool ngầu che mặt (che mặt thì giả dụ như đeo mặt nạ hoặc lấy cái gì đó che mặt ko phải là ko vẽ mặt )

mn ơi giúp mk vs mk đang cần gấp

2/ Viết phương trình hóa học của phản ứng giữa oxi với: a) Magie (Mg) b) Photpho (P) c) Butan (CH4) 3/ Tính thể tích khí oxi và thể tích không khí (đktc) cần thiết để đốt cháy: a) 1 mol cacbon b) 1,5 mol photpho Biết khí oxi chiếm 20% thể tích không khí. 4/ Đốt cháy 6,2 gam photpho trong bình chứa 7,84 (l) khí oxi (đktc) tạo thành điphotpho pentaoxit (P2O5) a) Photpho hay oxi, chất nào dư và dư bao nhiêu mol? b) Tính khối lượng điphotpho pentaoxit. 5/ Tính thể tích khí oxi (đktc) cần thiết để đốt cháy 1 kg than, biết than chứa 96% cacbon và 4% tạp chất không cháy. Tính khối lượng khí cacbonic sinh ra trong phản ứng. 6/ Người ta đốt cháy lưu huỳnh trong bình chứa 15 gam khí oxi. Sau phản ứng thu được 19,2 gam khí sunfurơ (SO2) a) Tính số gam lưu huỳnh đã cháy. b) Tính số gam oxi còn dư sau phản ứng. 7/ Em hãy giải thích vì sao: a) Khi càng lên cao thì tỉ lệ thể tích khí oxi trong không khí càng giảm? b) Phản ứng cháy của các chất trong bình chứa oxi lại mãnh liệt hơn trong không khí? c) Vì sao nhiều bệnh nhân bị khó thở và những người thợ lặn làm việc lâu dài dưới nước… đều phải thở bằng khí oxi nén trong bình đặc biệt? d) Củi, than cháy được trong không khí. Nhà em có củi, than xếptrong hộc bếp, xung quanh có không khí. Tại sao củi, than lại không cháy? cảm ơn các bạn

I. Choose the underlined word or phrase marked A, B, C or D) in each sentence that needs correcting. 1. If someone came into the store, smile and say, “May I help you?” A B C D 2. If you try these cosmetics, you look five years younger. A B C D 3. If you do not understand what were written in the book, you could ask Mr. Pike. A B C D 4.I will come to meet Mr. Pike and tell him about your problems if you didn’t solve them yourself. A B C D 5. Sam will not graduate unless he doesn’t pass all the tests. A B C D 6. If there isn’t enough food, we couldn’t continue our journey. A B C D 7. Unless you pour oil on water, it will float. A B C D 8. The assistant asked Helen whether those shoes was too small for her. A B C D 9. If anyone will phone, tell them I’ll be back at 11:00. A B C D 10. We can hire a minibus if there will be enough people. A B C D 11. If John make soup, he can chop the kohlrabi into chunks rather than slice it. A B C D 12. My mum might roast a chicken if she heard that you will come for lunch. A B C D 13. Unless you use a bottle of oil, you cannot deep-dry two kilos of chicken wing. A B C D 14. You must steamed the dim sum in thirty minutes, or else it is still raw. A B C D 15. If it is my birthday, my mum would simmer some kilos of beef bones to make broth. A B C D 16. You have eat nutritious things to stay healthy. A B C D 17. I fall in love with curry immediately and eat a small portion. I’m so full up now. A B C D 18. She was afraid that my mom would get angry because there were dark splash of mud on her skirt. A B C D 19. You have to improve your cooking skills if you want attend this cooking class. A B C D 20. What will happen if we cooked the dish too long? A B C D I. Complete the sentences based on the words given. You can add extra words or make changes. 1. If / you / come / Viet Nam / you / should / try / pho / . / It / really / delicious /. _____________________________________________________________________ 2. You / can’t / have / good / health / unless / exercise / more. _____________________________________________________________________ 3. You / should / stop / eat / sweets / if / want / have / toothache. _____________________________________________________________________ 4. Young / children / should / allow / watch / TV / more / 3 hours / day. _____________________________________________________________________ 5. Mai / can / concentrate / learning / unless / her / brother / stop / make / noise. _____________________________________________________________________ 6. Students / must / follow / school / rules / if / they / want / get / trouble. _____________________________________________________________________ 7. When / you / grow / up / you / will / know / importance / family / meals. _____________________________________________________________________ 8. We / should / skip / breakfast / because /it / important / health. _____________________________________________________________________ 9. Unless / she / change / diet / she / will / get / ill. _____________________________________________________________________ 10. If / Anna / busy / can / you / help / me / cook / curry? _____________________________________________________________________

Crops are sprayed with………………………………… to kill insects. a. fertilizer b. manure c. dung d. pesticide

Vì sao Dơi và Cá voi được xếp vào lớp Thú ? Trình bàynhững đặc điểm của Cá voi thích nghi với đời sống bơi lội trong nước ?