Предмет: Геометрия, автор: kalitkina2005

ЗАВТРА НАДО СДАТЬ помогите

Задача 2.

Приложения:

Ответы

Автор ответа: siestarjoki
1

BM - высота и медиана (ABC - р/б) => AM=12/2=6

BM =√(AB^2-AM^2) =8 (ABM, т Пифагора)

BD⊥(ABC) => BD⊥BM

DM =√(BD^2+BM^2) =10 (MDB, т Пифагора)

BD⊥(ABC), BM⊥AC => DM⊥AC (т о трех перпендикулярах)

S(ADC) =1/2 AC*DM =1/2 12*10 =60

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Night Work
Can you imagine what it would be like working at night? You would start your day when everyone else was going to bed, and you would go to bed when everyone else was getting up. Is that really a natural way to live?
These days more and more jobs need to be done at night. Most big hotels offer 24-hour room service, and need staff at reception and working in the bars. Many companies have 24-hour call centers to deal with emergency cases. There are 24-hour supermarkets, and of course there are the workers for the emergency services such as firefighters, the police and hospital workers.
However, few people can work well at night. This is partly because we cannot easily change our sleeping habits.
Some people can manage on as little as three hours’ sleep while others need as many as eleven hours- you are either a “short sleeper “ or a “long sleeper”. If working at night stops you from getting the amount of sleep you need, you will damage your health.
The best part of the day for everyone is around lunchtime and the worst point is between 2 a.m. and 4 a.m. So if you are driving home at this time or doing something important at work, things are far more likely to go wrong!
Humans are used to sleeping at night and being awake during the day, and they ‘ll never be able to do things the other way round. The problem is that today’s 24-hour society isn’t going to slow down, which means that night workers will remain.

Choose the best answer:
11. What is the writer’s main aim in writing the text?
A. To describe the importance of work.
B. To say that working at night can be bad for you.
C. To suggest that people can change their way of life.
D. To recommend people spend more time sleeping.
12. What is said about night jobs?
A. Many people refuse to work at night.
B. It is easier working at night than during the day.
C. There are better working conditions at night jobs.
D. There is a variety of them.
13. What would a reader learn about sleep from the text?
A. Everybody needs the same amount of sleep.
B. It’s difficult to change your sleeping needs.
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D. Many people need more than 11 hours’ sleep.
14. What does the writer say about the future?
A. Fewer people will work during the day.
B. Some jobs will always be done at night.
C. People will need fewer services.
D. People will work longer hours.
15. Which of the following could also be a title for this text?
A. A good night’s sleep can change your life! C. Society is changing but our bodies are not!
B. A worker that sleeps more, works more! D. The best jobs in the world!
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