Biết tan\(\alpha=3.\) Tính M =\(\frac{\sin\alpha.\cos\alpha}{\sin^2\alpha-\cos^2\alpha}\)

Chứng minh rằng giá trị của các biểu thức sau không phụ thuộc vào số đo góc nhọn \(\alpha\) :

B= \(\cos^2\alpha+\cos^2\alpha.\sin^2\alpha+\sin^4\alpha\)

C= \(\frac{1}{1+\sin\alpha}+\frac{1}{1-\sin\alpha}-2\tan^2\alpha\)

Cho \(\Delta\)ABC vuông tại A (AB < AC) đường cao AH và trung tuyến AM, đặt góc ACB =\(\alpha\). Chứng minh sin2\(\alpha\)= sin\(\alpha\) . cos \(\alpha\)

Cho hình vuông ABCD. Gọi H là một điểm nằm giữa A và B. Tia DH và tia CB cắt nhau tại K. Chứng minh rằng \(\frac{1}{DH^2}+\frac{1}{DK^2}\) không đổi khi H thay đổi trên cạnh AB.

Circle the letter A, B, C or D to indicate the sentence that is closest in meaning to the given one.

1. He did his homework, and then he watches TV.

A. Before he did his homework, and then he watched TV.

B. After he had done his homework, he watched TV.

C. Before he had done his homework, he watched TV.

D. By the time he did his homework, he watched TV.

2. The volunteers have rescued three cats.

A. Three cats have been rescued by the volunteers.

B. Three cats are rescued by the volunteers.

C. Three cats were rescued by the volunteers.

D. Three cats has been rescued by the volunteers.

3. In 2004, a tsunami suddenly destroyed a part of Indonesia.

A. A part of Indonesia is suddenly destroyed a tsunami in 2004.

B. A part of Indonesia was suddenly destroyed by by a tsunami in 2004.

C. A part of tsunami suddenly destroyed Indonesia in 2004.

D. Indonesia suddenly destroyed a tsunami in2004.

4. The strong winds last night scattered debris across the seaside.

A. Debris has been scattered across the seaside by the strong winds last night.

B. Debris is scattered across the seaside by the strong winds last night.

C. Debris was scattered across the seaside.

D. Debris was scattered across the seaside by the strong winds last night.

Choose the best answer A ,B, C or D to complete the sentences

1. We have to suffer ______ a lot of floods due to our serious destruction of forest.

A. to

B. on

C. from

D. with

2. Iwarned him ___ to close to the fire.

A. not to go

B. Not go

C. Didn't go

D. No going

3. I ____my English exercise before I went out.

A. Did

B. was doing

C. do

D. Had done

4. A heavy storm swept through the village and many people______.

A. are killed

B. were killed

C. kill

D. killed

5. He fell off the tree and_______.

A. was badly injured

B. was bad injured

C. was injured himself badly

D. badly injured

6. pollution is caused from the following sources , except ________.

A. Water from households

B. water in rivers

C. wastes house

D. chemicals

7. A new English center ______next year.

A. Opens

B. is opened

C. is opening

D. will be opened

Cho tam giác ABC vuông tại A, đường cao AH. Đường phân giác AD chia BC thành hai đoạn BD=36cm, CD=60cm .

a) Tính tỉ số \(\frac{HB}{HC}\)

B) Tính chiều cao AH

Cho tam giác ABC vuông tại A, đường cao AH. Cho \(\frac{AB}{AC}=\frac{5}{7}\), AH = 15cm. Tính độ dài HB và HC.

HELP MÌNH VỚI, MÌNH ĐANG CẦN GẤP

Qua văn bản Hoàng Lê nhất thống chí hồi thứ 14, em thấy những vẻ đẹp nào của vua Quang Trung? ( gạch ý + dẫn chứng)

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