найдите сумму первых двадцати членов арифметической прогрессии(аn)если а1=-7,а20=53

решить уравнение и сделать проверку.

х/3=17     49-х=28      64/х=4

Заполните пробелы с правильной формы слова в скобках

1. The hurricane caused terrible ______    in the area. (DESTROY)
2. You have to______   all the new books that arrive in the school. (CLASS)
3. I'm sorry, I think I'll be______      to attend the meeting. (ABLE)
4. She goes jogging every morning; she's really keen on physical______  (FIT)
5. _____, nobody was killed in the accident. (FORTUNE)
6. He's quite nice, but when he's angry he becomes very______  (FRIEND)
7. The Equator is an______  line drawn round the Earth. (IMAGINE)
8. I really like her. She's got a very lively ______ (PERSON)
9. Tell me the _____, I won't get angry. (TRUE)
10. She likes her students to be _____ and call her Miss Jones. (RESPECT)
11. You must take a_____  as soon as possible. (DECIDE)
12. _____" killed the cat." (CURIOUS)
13. I decline all_____  (RESPONSIBLE)
14. This design shows great_____  (ORIGINAL)
15.You're making the problem_____  hard for you. (NECESSARY)