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.
dear ann,
i'm very glad to hear you again. sorry for not writing for so long, i've been really busy at school.
so, you've written that you are going to visit *страна*. i'm happy to hear it! you should visit lost of places, my country is so big and beautiful! for, instance, *3-4 достопримечательности*. with no doubts you can stay at my place! me and my parents will be very happy to see you. the weather in june is usually very pleasant. however, it can be rainy or even cold, so take both warm and cold clothes.
write back soon, *имя*.
mobile phones are not allowed at school
you can't talk during exams
you can't wear jeans at school
you can't have lunch at home at school
you can't eat in class at school
you can't listen to music at school
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