C= $\frac{1}{3}$ +$\frac{1}{3^2}$ +...+ $\frac{1}{3^99}$ $\frac{1}{3}$ +$\frac{1}{3^2}$ +...+ $\frac{1}{3^99}$ (phân số cuối là 3^99 nha) Chứng minh: C < $\frac{1}{2}$

Cho tam giác abc vuông tại a có sin C= $\frac{1}{cos B}$ . Tính tỉ số lượng giác của hai góc trên

2. Put the verbs in the Past Simple or Past Perfect. 1. Karen (not want) to come to the cinema with us because she (already/ see) the film. 2. When the students (do) the experiment, they (write) a report on it. 3. “Was Tom at the party when you arrived?” - “No, he (go) out. 4. Sorry I’m late. The car (break) down on my way here. 5. I (take) the book back to the library when I (read) it. 6. Yesterday morning I (remember) the answer to the question Bob (ask) ___me the night before, so I (phone) him. 7. Last night, I (go) to Jim’s room and (knock) on the door but there (be) no answers. Either he (go) out or he (not want) to see anyone. 8. Angela asked me how to use the photocopier. She (never/ use) it before, so she (not/ know) what to do 9. I (live) in Texas for 4 years before I (move) California. 10. When Mr. Smith (wake) yesterday morning, breakfast (already be) ready. 11. Before I (get) promotion, I (work) very hard. 12. Yesterday, my mother (pick) me up from school before we (go) shopping together. 13. Our grandparent (tell) us that he (serve) in the army in 1945. 14. After having dinner with my boyfriend, I (go) in front of such large 15. Yesterday (be) the first time Jane (perform) audience. 16. Peter (admit) he (break) my favorite vase the day before. 17. What (you/ do) before you (come) there? 18. Yesterday I (feel) nervous as I (not prepare) my presentation carefully. 19. (Peter/ come) to see you after he (finish) his work? 20. When she (finish) her work, she (go) to the cinema.

thực hiện phép tính (x^2-x^3).(x-5) (2x+y^2)(2x-y^2)

Các bạn giúp mik nhanh nha mik đang cần gấp

giup nha moi nguoi help!!!!!!!!!!!!!!!!!!!!!

hòa tan ag hh (cuo và fe2o3) trong dd hcl dư tạo thành dd chứa 2 muối có nồng độ mol bằng nhau . tính % khối lượng của các chất trong hh ban đầu

Cảm ơn trước ==================

M.n ơi giúp mình với mình đang cần gấp ạ cảm ơn nhìu

Phân tích đa thức sau thành nhân tử.20x^4y^2-20x^3y^3+5x^2y^4