Một thấu kính hội tụ có tiêu cự 30 cm. Vật sáng AB đặt vuông góc với trục chính của thấu kính. Ảnh của vật tạo hởi thấu kính ngược chiều với vật và cao gấp ba lần vật. Vật AB cách thấu kính

A. 15 cm.

B. 20 cm.

C. 30 cm

D. 40 cm.

Underline the mistake and rewrite the correct sentence.

1. What is the matter to your friend?

=> with

2. I am at my friend's birthday party last weekend.

=> was

3. Nhung watchs TV every evening.

=> watches

4. How many book do you have?

=> books

5. Elephants are smaller than monkeys.

=> bigger

Choose the odd one out.

1.a. went b. played c. bought d. talk

2.a. last week b. tomorrow c. yesterday d. last month

3.a.cook b. clean c. watch d. beautiful

4.a. eyes b. headache c. toothache d. fever

5.a. badminton b. football c. music d. volleyball

Change the following sentences, using the structure SUCH + NOUN + THAT.

1. The weather was so hot that all the races were cancelled.
=> It was such hot weather that all the races were cancelled.

2. My hometown is so lovely that I always want to live and work there.
=> It is such a lovely hometown that I always want to live and work there.

3. Her garden is so beautiful that we want to pay it a visit.
=> She has such a beautiful garden that we want to pay it a visit.

4. The novel is so interesting that I read it again and again.
=> It's such an interesting novel that I read it again and again.

5. The baby is so cute that his mother wants to kiss him over and over.
=> He's such a cute baby that his mother wants to kiss him over and over.

6. The father is so strict that his children never dare to talk to him.
=> He's such a strict father that his children never dare to talk to him.

7. My friends are so nice that I feel comfortable to be with them.
=> They are such nice friends that I feel comfortable to be with them.

Mỗi đường thẳng cắt \(\text{2009 }\) đường thẳng còn lại tạo nên \(\text{2009 }\)giao điểm .

Mà có 2010 đường thẳng nên sẽ có : \(\text{2010.2009=4038090}\) (giao điểm )

Nhưng mỗi giao điểm lại được tính 2 lần  nên số giao điểm thực tế là :

\(\text{4038090 : 2=2019045}\)( giao điểm)

Vậy có \(\text{2019045}\) giao điểm.