Đặt `A= 1/2^2 + 1/3^2 + 1/4^2 +...+ 1/99^2`
Ta có:
`1/2^2 = 1/2.2 < 1/1.2`
`1/3^2 = 1/3.3 < 1/2.3`
`1/4^2 = 1/4.4 < 1/3.4`
`................`
`1/99^2 = 1/99.99 < 1/98.99`
`=> 1/2^2 + 1/3^2 + 1/4^2 +...+ 1/99^2 < 1/1.2 + 1/2.3 +1/3.4 +...+ 1/98.99`
`=> A< 1/1 - 1/2 + 1/2 - 1/3 +...+ 1/98 - 1/99`
`=> A< 1 - 1/99 < 1`
Vậy `A<1`
Đáp án + Giải thích các bước giải:
`1/2^2+1/3^2+1/4^2+...+1/99^2<1/1.2+1/2.3+1/3.4+...+1/98.99=1-1/2+1/2-1/3+1/3-1/4+...+1/98-1/99=1-1/99<1`
Vậy `1/2^2+1/3^2+1/4^2+...+1/99^2<1`
XI. Make meaningful sentences based on the given words. 1. Number/ people/ this/ small area/ be/ increase/ quickly/ next/ 20 years. ............................................................................................... 2. Solar energy/ be/ consider/ one/ most/ important/ energy sources/ future. ............................................................................................... 3. Your car/ run/ fast/ than/ mine/ not? ............................................................................................... 4. New/ means/ transport/ be/ introduce/ future. ............................................................................................... 5. Today/ there/ be/ little/ traffic/ yesterday. ...............................................................................................
Vẽ cho mình một con chim phượng hoàng lửa đang giãy giụa trong biển lửa.
X. Read the passage and then answer the questions. Viet Nam is a country in the South – East Asia. It has an area of 329,566 sq.km. Hanoi is the capital and Ho Chi Minh City is the largest city. The population of Viet Nam is about 80 million. It has age-old culture and long tradition of fighting against foreign invaders. Viet Nam is now a member country of ASEAN and many other international organizations such as APEC, WTO... Viet Nam exports rice, coffee and many other farm products. Viet Nam has lots of tourist attractions and World Heritage Sites such as Ha Long Bay, Phong Nha Cave, Hoi An Ancient Town, My Son Sanctuary, etc. Vietnamese people are proud of their country. They have been trying hard to build a powerful and prosperous country. Answer the questions: 1. Where is Viet Nam located? ....................................................................................................................... 2. What is the area of Viet Nam? ....................................................................................................................... 3. What does Viet Nam export? ....................................................................................................................... 4. What have Vietnamese people been trying to do? ....................................................................................................................... 5. Name some World Heritage Sites in Viet Nam. .......................................................................................................................
Viết một đoạn văn về chủ đề quê hương ,trong đó sự dụng một số thành ngữ,tục ngữ đã tìm được
Nếu 2 vòi nước cùng chảy vào 1 bể thì sau 4h48p sẽ đầy bể .Nếu chỉ mở cho mỗi vòi chảy một mình thì vòi thứ nhất chảy chậm hơn vòi thứ 2 là 4h. Hỏi mỗi vòi chảy một mình thì sau bao lâu sẽ đầy bể?
Giusp mình điiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
giúp mình đi màaaaaaaaaaaaaaaaaaaaaaaa
VẼ ĐẬU MẦM ....................................
IX. Read the passage and choose the correct answer. Well, here I am in Peru on our South America tour. I went on the trip with some best friends of mine. We had a good journey. It took three days by bus, but we saw a lot of things on the way. We didn’t do much for the first two days, as a couple of the other guys were ill. We spent most of the time on the beach. (They are OK now!). On Wednesday, we came up to the mountains, and yesterday we went to the old Inca city of Machu Picchu and did some sightseeing. It was fantastic! We did have a lot of time there, but we saw everything and I took a lot of photos. 1. Where was the author? A. In Peru. B. In Africa. C. In South America. D. A & C are correct 2. The author went there ...................... A. by himself/ herself B. with some friends C. with his/ her best friend D. with his/ her brother 3. The author went there by ...................... A. taxi B. bus C. motorbike D. train 4. What does the word “They” in line 4 mean? A. days B. things C. the guys who are ill D. most of the time 5. What did they do? A. They spent most of the time on the beach. B. They came up to the mountains. C. They went to the old Inca city of Machu Picchu. D. All are correct.
VIII. Read the passage and choose the correct answer. Easter is an important Christian festival and holiday. It is (1) ......................... to celebrate the resurrection of Jesus Christ. People celebrate Easter (2) ......................... the world. In the UK, Easter is a public holiday. People (3) ......................... Easter chocolate eggs to their friends and family. In the US, Easter is a (4) ......................... holiday. People can go to church and have a special family meal. In Russia, Easter is one of the (5) ......................... important holidays. People celebrate it with an Easter breakfast or meal. 1. A. made B. held C. given D. opened 2. A. through B. in C. all D. around 3. A. eat B. have C. give D. receive 4. A. nation B. local C. native D. national 5. A. more B. best C. most D. better
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