Cho tam giác nhọn ABC, có AB<AC, đường cao AH. Chứng minh:

a) C/m góc BAH < góc HAC.

b) Trên đoạn HC lấy điểm D, sao cho HD=HB. C/m tam giác ABD cân.

c) Từ D kẻ DE vuông góc AC, từ C kẻ CF vuông góc với AD. C/m rằng ba đường thẳng AH, DE, CF cùng đi qua một điểm.

Các bạn làm giúp mình ạ. Mình cảm ơn!

Bài 1: Cho f(x) = 2x⁶ + 3x² + 5x³ - 2x² + 4x⁴ - x³ + 1 - 4x³ - x⁴

a) Thu gọn f(x)

b) Tính f(1); f(-1)

c) Chứng tỏ f(x) không có nghiệm

Bài 2: Tìm nghiệm của các đa thức:

a) f(x) = 5x - 10

b) g(x) = 2x - ½

c) P(x) = x² - 5x - 6

d) Q(x) = x² - 4x

Các bạn làm giúp mình với nhé. Mình cảm ơn.

I. Choose the correct answer:
1. Do you mind...the air - conditioner? It is too cold.
A. turn on B. turn off C. turning on D. turning off
2. Sitting too long in front of he computer makes your eyes.....
A. tired B. harm C. boring D. relax
3. When you plays games online, be careful when you make friend with.....
A. girls B. boy C.strangers D. your classmates
4. Anna prefers.....TV to.....books.
A. watching/reading B. watch/read C. watching/read D. watch/reading
5. The phrase " window shopping " means:
A. buying a window B. just looking without intending to buy
B. going shopping through the window D. buying so many things at the same time
6. Do you fancy.....origami?
A. making B. make C. doing D. do
7. The sentence " c u 2moro " means:
A. See you tommorrow B. Nice to meet you
C. See you later D. Let me see
8. I hate.....up late to do homework.
A. staying B. stay C. get D. getting
9. My younger brother used to detest.....fish, but now he likes doing it.
A. eats B. ate C. eating D.eat
10. Computers should only be used for....time.
A. limited B. unlimited c. limit D. freedom
II. Read the passage about British and American teenagers, and answer the questions:
Sport: In the UK, footbal, rugby, tennis and basketball are the most popular sports for teenagers. In the USA, American football, athletics, basketball and baseball are popular.
The Internet and television: Teenagers in both the UK and the USA today watch television less than before but they use the Internet more. They spend over 25 hours a week online. Pocket money and shopping: The average teenager in the UK gets about 7$ a week pocket money. In the USA it is about. They spend their money on clothes and going out, but magazines, presents and snacks are so important.
Friends: The average British and America teenagers has seven close friends. He or she has sixteen online friends on social network websites.
1. Which sports do British and American teenagers play in their free time?
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2. How long do they spend online?
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3. How much pocket money do they get?
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4. What do they spend it on?
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5. How many online friends do they have?
III. Complete the sentences in Mai's email with the correct form of the verb in brackets:
Hi, Susan!
Well, I'm here in Ha Noi, now. I see quite a lot of my cousin Hoa because we (1) (enjoy/do)................ the same things. I have some new friends called David and John. David is very good at computers and he (2) (not mind/help).............me so that's good. John is really nice too. He (3) (play)...........basketball and he (4) (go/skateboard)............ quite a lot. His brother Toby is 18 and he's really cool but he (5) (prefer/play)............football. I (6) (do)...............gymnastics once a week and Hoa (7) (do)..........karate. She prefers indoor sports because she (8) (not like/get)........cold!
Write soon!
*Các bạn làm giúp mình với ạ, mình đang cần gấp! Mình cảm ơn trước nhé!