B ạ

2B, 3C, 4D, 5A,6B,7C

4n²+14n+7=(n+3)(4n+2)+1

Do n thuộc Z+ => 4n2+14n+7 và n+3 là hai số nguyên tó cùng nhau

=> 4n2+14n+7 và n+3 là hai số chính phương

Do n thuộc Z+ => (2n+3)² ≤ 4n²+14n+7<(2n+4)²

                        => 4n² + 14n+7= (2n+3)² => n=1 => là số chính phương

Thử lại với n=1 => A=100 (thỏa mãn)

- Bước 1: Phản ứng với Cu(OH)2:

glycerol: tạo dung dịch màu xanh lam đặc trưng.

ethanol và benzyl alcohol: Không có phản ứng 

- Bước 2. Phản ứng với dung dịch KMnO4:

benzyl alcohol: Bị oxy hóa thành axit benzoic

ethanol: Phản ứng chậm hơn.

Lớp Hình nhện 

16:A

17:B

18:A và B

1. Dalat is famous for its sceneries.
2. I go to the cinema every week.
3. The artisan is carving a statue skillfully.
4. This workshop was set up on the river bank years ago.
5. Foreign tourists often visit Ben Thanh Market for souvenirs.
6. Where did you buy this knitted tablecloth?

1. The 'craftsmen worked in a 'freezing 'cold 'workshop.
2. The street is full of 'vendors 'selling 'handicrafts.
3. The town sur'vives 'mainly through 'tourism.
4. Inde'pendence 'Palace is a 'major 'tourist at'traction.
5. They sell rugs made by 'local arti'sans.
6. Do you know about the 'other 'services a'vailable at your 'local 'library?

1. conical hat 2. paintings 3. lacquerware 4. pottery 5. lanterns 6. silk 7. drums 8. marble

Tham khảo !!!

Independent learning often involves self-study - learning at home without a teacher. Let's explore the benefits and drawbacks of this approach.

Firstly, self-study empowers learners to take control of their education. They can delve into subjects that interest them deeply and explore at their own pace. Secondly, it fosters a sense of self-reliance and resourcefulness. Learners develop problem-solving skills as they navigate through challenging concepts independently. Finally, self-study can be cost-effective, as learners can access a wealth of free resources online.

However, learners may struggle with self-motivation and consistency. Without external accountability, it's easy to procrastinate or lose focus. Additionally, self-study lacks the interactive element of traditional classroom learning. Learners miss out on valuable opportunities for discussion, feedback, and collaboration with peers and teachers.

In conclusion, self-study offers flexibility and autonomy, but it also presents challenges in terms of motivation and interaction. Learners should strike a balance between self-directed learning and seeking support when needed. By embracing the benefits and addressing the limitations, individuals can harness the power of self-study to achieve their educational goals effectively.