Предмет: Алгебра, автор: isnsj

Помогите пожалуйста

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Автор ответа: MrSolution

Ответ:

Объяснение:

d=7 (из условия)

$a_4=a_1+3d\\a_4=9+21=30$

Возможно другое, менее оптимальное, но тоже допустимое решение:

$a_4=a_3+7\\a_3=a_2+7\\a_2=a_1+7\\=>a_3=a_1+14\\a_4=a_1+21\\a_1=9\\=>a_4=9+21=30$

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Misha: What's wrong, Emily? Where are you going?
Emily: My friend Jane's parents have just phoned and said that she has been taken to hospital.
Rob: But what's happened to her? Do they know?
Emily: They don't, but I do. And I feel so guilty because I didn't tell her parents earlier.
Rob: But what is it?
Emily: OK. I think I'll have to tell you.

My friend Jane has always had low self-esteem.
Sometimes she was unhappy with her eyes; other days she didn't like her nose. Once she told me that she hated herself, but I just laughed.
Last year things started to get worse because Jane had gained a bit of weight. It wasn't a lot but she got upset because she thought that everybody was looking at her. She thought that she was fat. I told her that she was perfectly normal, but she didn't listen. She said that she would only be happy if she was as thin as a supermodel.
Then she started to lose weight. Every week she was getting thinner and thinner. I noticed that she didn't eat her school lunch and she didn't go out with our gang when we went to our local pizzeria. When we asked her to come, she always said that she had just eaten and wasn't hungry. When I asked her if she was on a diet, she always said that she wasn't. When I left for England, Jane was a size 6. We kept in touch by e-mail and she wrote to me that she was all right. From her letters I also knew that she had joined our local drama club and was going to be an actress after school. I was happy for her and thought that she had forgotten all that nonsense about dieting.
We met again three weeks ago when I came back from England. I didn't recognise her. She was pale, thin and a size 2! At first, I thought that she was ill, but then I noticed something: we had spent the whole day together and she hadn't eaten anything. It was then I realized what had happened to my friend. I was going to phone her parents but then I thought that it wouldn't be right.
Misha: I understand. You felt that you'd let your friend down if you told on her.
Emily: Yes, that's what I thought.
Mark: How could you be so stupid, Emily? Do you remember the girl from our school, who was expelled last year?
Emily: Yes, I remember. It was Kate Ferguson. But why was she expelled?
Mark: She had the same problem as your friend Jane. She thought that she was fat and started dieting. In the end she got very thin but she still thought that she was fat and couldn't eat at all. It's a disease called anorexia. It's very dangerous and a lot of young people die from it.
Emily: But why was she expelled?
Mark: The teacher found out that she had been setting a bad example. Other girls also decided to start dieting and stopped eating. Fortunately, they hadn't become ill by the time it all came out.
Emily: That's awful. What should I do now?
Misha: I think we should phone her parents and tell them the truth if it's not too late.5

Complete the sentences with the information from the text.
Model: Emily was worried because her friend Jane's parents had phoned
       and said... — Emily was worried because her friend Jane's parents
       had phoned and said that she had been taken to hospital.
      1.   Emily knew that Jane had very low self-esteem because once Jane had told her...
2.   Jane got upset because she thought...
3.   When the girls invited Jane to the pizzeria, she always said...
4.   When Emily asked Jane..., Jane always replied...
5.   When Emily was in England, Jane wrote to her that...
6.   When Emily read those letters, she thought that...
7.   Emily realized that Jane... when they met again.

6   Who said these words? Observe the sequence of tenses in your answers.'
Model:"I feel guilty." — Emily said to her friends that she felt guilty.
         "What's wrong?" — Mark asked what was wrong.

1.   "When I left for England, Jane was a size 6."
2.   "We should phone her parents and tell them the truth."
3.   "Why was she expelled?"
4.   "I'll only be happy if I'm as thin as a supermodel."
5.   "I hate myself."
6.   "Are you on a diet?"
7.   "Do you remember the girl from our school, who was expelled last year?"
8.   "We kept in touch by e-mail."