решение. 1. ri=2*r; rii=r/2; ri/rii=4; не надо ни о какой площади сечения говорить. два куска проволоки содинили последовательно, получили ri=2*r; два куска той же проволоки соединили параллельно, получили rii=r/2; ну, а теперь раздели первое на второе!
а теперь общий случай: ri=r*n; rii=r/n; ri/rii=n^2; кусок проволоки разрезали на n одинаковых кусков. сначала эти куски соединяют последовательно: ri=r*n; затем соединяют параллельно rii=r/n; ну и дели первое на второе и делай выводы.
1) I knew that he was dissatisfied with the results of my work.
2) We were informed that tomorrow was declared non-working.
3) At the interview, I said that I am very interested in the work of the system
administrator.
4) He said that the company has been exporting wool since 1985.
5) I was afraid that he would be angry if I did not arrive on time.
6) Everyone agrees that the company's work last year was effective.
7) She says she knows two foreign languages.
8) He said he would be back very soon.
9) Our guide said that the bus has just arrived and will leave in an hour.
10) We hope that they will discuss this issue as soon as the director returns
to Moscow.
13. - C
14. - B
15. - C
16. - A
17. - B
18. - B
19. - B
20. - C