​Ta có: \(1^{2} + 2^{2} + 3^{2} + \ldots + 1 0^{2} = 385\)

Suy ra: \(\left(\right. 1^{2} + 2^{2} + 3^{2} + \ldots + 1 0^{2} \left.\right) . 3^{2} = 385. 3^{2}\)

\(\left(\right. 1.3 \left.\right)^{2} + \left(\right. 2.3 \left.\right)^{2} + \left(\right. 3.3 \left.\right)^{2} + \ldots + \left(\right. 10.3 \left.\right)^{2} = 385. 3^{2}\)

Do đó \(A = 3^{2} + 6^{2} + 9^{2} + \ldots + 3 0^{2} = 3465\).

a) A=(2/7.1/4-1/3.2/7):(2/7.3/9-2/7.2/5)

A=[2/7(1/4-1/3)]:[2/7(1/3-2/5)]=(1/4-1/3):(1/3-2/5)=1 1/4

b) B=51​(72​+31​)−31​(72​+31​)43​(51​−72​−31​+72​)​=(51​−31​)(72​+31​)43​(51​−31​)​=15211​.

Bước làm:

Bước 1: Đưa số hữu tỉ về dạng phân số.

Bước 2: Đưa phép chia về dạng phép nhân các phân số.

Bước 3: Áp dụng tính chất của phép nhân các phân số: Bao gồm giao hoán, kết hợp, phân phối với phép cộng (trừ).

a) \(A = \frac{3}{5} . \&\text{nbsp}; \frac{6}{7} + \frac{3}{7} . \&\text{nbsp}; \frac{3}{5} - \frac{2}{7} . \&\text{nbsp}; \frac{3}{5}\)
\(= \frac{3}{5} \cdot \left(\right. \frac{6}{7} + \frac{3}{7} - \frac{2}{7} \left.\right) = \frac{3}{5}\)
b) \(\&\text{nbsp}; B = \left(\right. - 13 \cdot \frac{2}{5} + \frac{- 2}{9} \cdot \frac{2}{5} + \frac{2}{5} \cdot \frac{11}{9} \left.\right) \cdot \frac{5}{2}\)
\(= \left(\right. - 13 - \frac{2}{9} + \frac{11}{9} \left.\right) \cdot \frac{2}{5} \cdot \frac{5}{2} = - 13 + \left(\right. \frac{11}{9} - \frac{2}{9} \left.\right) = - 12.\)
c) \(C = \left(\right. \frac{- 4}{5} + \frac{5}{7} \left.\right) \cdot \frac{3}{2} + \left(\right. \frac{- 1}{5} + \frac{2}{7} \left.\right) \cdot \frac{3}{2} = \left(\right. \frac{- 4}{5} + \frac{5}{7} + \frac{- 1}{5} + \frac{2}{7} \left.\right) \cdot \frac{3}{2} = \left(\right. \left(\right. \frac{- 4}{5} + \frac{- 1}{5} \left.\right) + \left(\right. \frac{5}{7} + \frac{2}{7} \left.\right) \left.\right) \cdot \frac{3}{2} = 0.\)
d) \(D = \frac{4}{9} : \left(\right. \frac{1}{15} - \frac{10}{15} \left.\right) + \frac{4}{9} : \left(\right. \frac{2}{22} - \frac{5}{22} \left.\right)\)
\(= \frac{4}{9} : \frac{- 3}{5} + \frac{4}{9} : \frac{- 3}{22} = \frac{4}{9} \cdot \frac{- 5}{3} + \frac{4}{9} . \&\text{nbsp}; \frac{- 22}{3}\)
\(= \frac{4}{9} \cdot \left(\right. \frac{- 5}{3} + \frac{- 22}{3} \left.\right) = \frac{4}{9} . \&\text{nbsp}; \frac{- 27}{3} = - 4.\)

Today I will talk about topic 1 is : Talk about your hobbies. So let's go!

My favorite hobby is singing, dancing, play the violin and piano and I like doing that activities because that's my favorite hobby and my future job to so I like doing them. I usually do it in the afternoon and when I have freetime because my study schedule is quite busy, I usually do those things when I have free time.And you know why I like doing those activities?Because in 2031, when I am in 12th grade, I will take the entrance exam to the People's Public Security School of Culture and Arts.My speech ends here. Thank you for reading this article.

1. My full name is Doan Ngoc Hoang Nghi

2. My favorite hobby is singing, dancing. I usually do it

3. My favorite song is all Kpop and Vpop song. I like it because it makes me more happy

4. I reduce trash by doing lots of things I don't really remember and I think it's really important

5. My favorite subject is music, P.E and art

1. 

Hi Ariana,

I hope you are doing well! I want to invite you to a concert this Saturday. It will be at the park, and the music will be fun! The concert starts at 5 PM. We can meet at my house at 4:30 PM and go together. It will be great to enjoy music and dance with friends. Let me know if you can come!

Best,
Kim

2. 

Dear Cafeteria Manager,

I hope you are well. I want to ask for healthier food options in our school cafeteria. Many students want fruits, salads, and whole grains. Healthy food will help us feel good and learn better. It is important for our health. Please consider adding more healthy meals to the menu. Thank you for listening!

Sincerely,

Tran Hoang

3. 

The movie "Toy Story" is a fun animated film. It is about toys that come to life when people are not around. The main character is Woody, a cowboy toy. He is best friends with Buzz Lightyear, a space ranger toy. They go on many adventures together. The story is funny and exciting, and it teaches us about friendship and teamwork. I really enjoyed watching this movie with my family!

1. His brother goes to the theater once a/per month. 

2. I usually store onions in a basket on the kitchen shelf.

1. It’s not a good idea to eat large meals right before bedtime. 

→ You shouldn’t eat large meals right before bedtime. 

2. He spends two hours a day reading books about adventure.

→ It takes him two hours a day to read books about adventure. 

3. Do you want to buy tickets for the concert?

→ Would you like to buy tickets for the concert?

1. Let's collect old textbooks to give to children in mountainous areas

2. My sister is fond of making vlogs about animals

3. Last week, I had a sore throat, so I stayed at home

1. My brother ate something bad and he had/got a stomach ache.

2.Why don’t we organize a talent show to raise money? 

3.You shouldn’t eat junk food every day.

4.I prefer listening to country music to listening to classical music.