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.
Відповідь:
- There __were___ no taps in the kitchens in the past. 2. There __were___ lots of dinosaurs in the worlds years ago. 3. There __is___ the Moon on the sky now. 4. There __were many e- mails in your box yesterday. 5- How many phones were___ there on the table in the morning? 6.There __are__ lots of projects to finish today. I'm so busy now. 7. There __was_ a noise in the garden last night.l was so scared. 8. There__is_ a black cat on the tree now. Can you see it? 9. How many girls __were __ there in your class last year? 10.There __was__ a big truck on the road last night. 11. There _were__ many people in the shopping centre last weekend. 12. There ___is_ an expensive car in front of your house now. Whose car is it? 13. There __was___ a radio in our home long time ago. 14-There _are_ lots of new dresses for you on your bed now. 15-There_was__ a beautiful horse on that tarm yesterday. 16-There__are__ lots of dirty socks on your bed now. Please put them into the machine. 17-There_were__ old photos on your mirror yesterday. Where are they now? 18-There _is__ an interesting lamp on your desk. I love it! 19- There__were__ strange people in your party last night. 20-There __are_ many new songs on my listen now. Would you like to listen? 21-There_were_ two sandwiches on the table five minutes ago. Where are they now? 22-There__is__ a dog in front of our house now. I think it's lost. 23-There__was_ only one cinema in out city five years ago. 24-There__is_ a camera in your car. Is that mine? 25-There_were__ many different animals in the wild many years ago. 26-There_were__ only three shops in our town ten years ago. 27-There__are__ lots of beautiful flowers in the vase. They smell amazing. 28-There___are___ many endangered animals in the world now. 29-There___is__ a new scooter for you in your room now. 30-There_were__ many different hobbies in the past.
Complete using the correct form of the phrasal verbs given.
call off, carry on, carry out, catch up (with)
1. Mike has been ill for a week. He will have to work really hard to catch up with his class.
2. The match was___called off__ due to bad weather.
3. He will never __catch up with__me. I am a far running faster.
4. After her coffee break, she__carried on__ writing her report.
5. Studies__carried out__ by the World Health Organisation indicate that cities are getting much noisier.