Đáp án:
Giải thích các bước giải:
`A = 3 + 3^2 + 3^3 +...+ 3^99`
`3A = 3^2 + 3^3 + 3^4 + ... + 3^100`
`3A - A = ( 3^2 + 3^3 + 3^4 + ... + 3^100) - ( 3 + 3^2 + 3^3 +...+ 3^99 )`
`2A = 3^100- 3`
⇒`2A = 3^100 - 3 + 3 = 3^100`
Vậy `n = 100`
Xin cho hay nhất
`A=3+3^2+3^3+3^4+...+3^99`
`3A=3^2+3^3+3^4+...+3^100`
`3A-A=3^100-3` (Ta sử dụng phương pháp khử)
Hay `2A=3^100-3`
Theo đề ta có :
`2A+3=3`
Thay vào ta có:
`3^100-3+3=3^n`
⇒`3^100=3^n`
⇒`n=100`
Help me với ạ. Chọn đáp án đúng,cần có lời giải thchs tại sao chọn đáp án đó 1. I couldn't help at his jokes. A. laugh B. laughing C. to laugh D. laughed 2. Tom offered Jane a ticket to the theater, but she refused to take it. A. to give B. give C. giving D. to be given 3. Those workers stopped their coffee because they felt tired from their new work. A. drink B. drank C. drinking D. to drink 4. He asked them A. help him B. should help him C. to help him D. help to him 5. Mr Minh advised my family leaving Vietnam. A. to think B. not to think C. against D. against to 6. I hope that woman again. A. to see B. of seeing C. seeing D. have seen 7. She wasted much time her old pair of shoes. A. mend B. to mend C. mending D. to be mended 8. He regrets lazy last year. He lost his job. A. to be B. be C. been D. being 9. She remembered that woman last month. A. of seeing B. to see C. seeing D. have seen 10. David tried his best , but his girlfriend refused B. explaining; to listen B. explaining; listening C. to explain; to listen D. to explain; listening 10. We heard a baby in a neighbouring village. A. cry B. to cry C. cried D. to crying 11. Willy denied a whole bag of chocolate chip cookies before lunch. A. eat B. to eat C. having eaten D. eaten 12. I was delighted my old friends again. A. to see B. seeing C. seen D. to be seen 13. We regret you that we cannot approve your suggestion. A. inform B. to inform C. informing D. informed 14. Have you ever considered a pharmacist? A. become B. becoming C. to become D. became 15. You had better at home until you feel better. A. staying B. stayed C. to stay D. stay 16. I remember my mother said the grass in the garden needed . A. to hear; cutting B. hear; cut C. heard; to cut D. hearing; cutting 17. My teacher doesn't allow us while he is explaining the lesson. A. talk B. to talk C. talking D. talked 18. We have plenty of time. We needn't A. hurry B. to hurry C. hurrying D. hurried 19. I promised on time. I mustn't late. A. be; be B. to be; to be C. to be; be D. be; to be
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