I là điểm nào?

A và C đều đúng nhé 

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Đây cũng là một ý tưởng hay đó em ah. Chúc các em phát triển nhóm và cùng giúp nhau trong cuộc sống, sẽ chia và giúp đỡ nhau cùng tiến bộ. Thân mến!

tiếc quá em 2011

\(CH_3COOCH_3+NaOH\rightarrow CH_3COONa+CH_3OH\\ n_{NaOH}=n_{CH_3COOCH_3}=\dfrac{7,4}{74}=0,1\left(mol\right)\\ Vậy:a=m_{ddNaOH}=\dfrac{0,1.40.100}{4}=100\left(g\right)\)

Thiên hà là một hệ thống lớn các thiên thể và vật chất liên kết với nhau bằng lực hấp dẫn, bao gồm sao, tàn dư sao, môi trường liên sao chứa khí, bụi vũ trụ và vật chất tối, một loại thành phần quan trọng nhưng chưa được hiểu rõ

Thiên hà là một hệ thống lớn các thiên thể được liên kết với nhau bằng lực hấp dẫn

    In today's digital age, screens have become an integral part of our daily lives. However, excessive screen time can have some negative impacts on our health, particularly for teenagers. In my opinion, it is important to limit teenagers' screen time. Firstly, prolonged exposure to screens has been linked to a variety of health problems such as obesity, poor eyesight, and insomnia. Spending excessive amounts of time in front of screens can also cause headaches, neck and back pain, and postural problems. Limiting teenagers' screen time can help ensure that they get enough physical activity, fresh air, and quality sleep that their growing bodies need. Secondly, excessive screen time can negatively impact teenagers' mental health. It can lead to feelings of isolation, anxiety, depression, and even addiction. Social media platforms, for instance, can create unrealistic expectations for youth, leaving many feeling inferior and depressed. To combat this, teenagers should learn to moderate their Internet and screen usage, and pursue more meaningful and fulfilling activities. Thirdly, screen time can affect teenagers' cognitive development. The brain of a teenager is still developing, and research shows that excessive screen time can impede brain development that affects cognitive skills such as attention span, memory, and problem solving. In contrast, spending more time reading, interacting face-to-face with peers, and engaging in outdoor activities can help teenagers build positive cognitive skills. In conclusion, while screens are useful tools, they should be used in moderation, especially for teenagers. Limiting their screen time can have positive effects on their physical, mental, and emotional well-being. Parents and guardians should encourage teenagers to find other activities that they enjoy besides screens such as sports, arts, traveling, and socializing with peers. By doing so, teenagers can strike a healthy balance between screen time and other activities, leading to a healthier and happier life.

a) \(\dfrac{1}{\tan\alpha+1}+\dfrac{1}{\cot\alpha+1}\) \(=\dfrac{\tan\alpha+1+\cot\alpha+1}{\left(\tan\alpha+1\right)\left(\cot\alpha+1\right)}\) \(=\dfrac{\tan\alpha+\cot\alpha+2}{\tan\alpha\cot\alpha+\tan\alpha+\cot\alpha+1}\) \(=1\) (vì \(\tan\alpha\cot\alpha=1\))

b) \(\cos\left(\dfrac{\pi}{2}-\alpha\right)-\sin\left(\pi+\alpha\right)\) \(=\sin\left(\alpha\right)-\sin\left(\pi-\alpha\right)\) \(=0\) (do \(\sin\) của 2 cung bù nhau thì bằng nhau, \(\cos\) của 1 góc bằng \(\sin\) của góc phụ với nó).

c) \(\sin\left(\alpha-\dfrac{\pi}{2}\right)+\cos\left(-\alpha+6\pi\right)-\tan\left(\alpha+\pi\right)\cot\left(3\pi-\alpha\right)\)

\(=\cos\left(\pi-\alpha\right)+\cos\left(-\alpha\right)-\tan\alpha\cot\left(\pi-\alpha\right)\)

\(=\tan\alpha\cot\alpha\) \(=1\) (ở đây áp dụng tính chất của 2 cung hơn kém \(\pi\) nhiều lần)

Dear Anna,

I'm glad that you like the cooking book. It has many interesting recipes in there, you should try one. By the way, Sunday sounds great, I'll come over at 4 p.m. 

See you soon,

     Linda

Hi Anna,

I'm glad that you're finding my book on healthy cooking helpful.

I am delighted to join you at your home this Sunday to find out some recipes from the book with you.

Unfortunately, my mango trees has not produced any mangoes at the time, but by the way I will buy some fresh mangoes from the market on the way to your place for one of the dishes.

Looking forward to seeing you soon.

Warm regards.

Linda.