Задачка.
Через точку А к окружности проведены касательная АВ (точка В лежит на окружности) и секущая, которая пересекает окружность в точках Е и F и проходит через центр окружности. Найти радиус окружности,если АВ = 12 , а АF=18.

Вообще какова формула радиуса? И как его найти по данным : "АВ = 12 , а АF=18."

ответить на вопросы The climate in Great Britain is mild and temperate due to the influence of the Gulf Stream. The British often say: "Other countries have a climate; in England we have weather." The weather in Britain is very changeable. A fine morning can change into a wet afternoon and evening. And a nasty morning can change to a fine afternoon. That's why it is natural for the British to use the comparison "as changeable as the weather" of a person who often changes his mood or opinion about something. The British also say that they have three variants of weather: when it rains in the morning, when it rains in the afternoon or when it rains all day long. The weather is the favourite conversational topic in England. When two Englishmen meet, their first words will be "How do you do?" or "How are you?" And after the reply "Very well, thank you; how are you?" the next remark is almost certain to be about the weather. When they go abroad the British often surprise people of other nationalities by this tendency to talk about the weather, a topic of conversation that other people do not find so interesting. The best time of the year in Britain is spring (of course, it rains in spring too). The two worst months in Britain are January and February. They are cold, damp and unpleasant. The best place in the world then is at home by the big fire. Summer months are rather cold and there can be a lot of rainy days. So most people who look forward to summer holidays, plan to go abroad for the summer — to France, Spain or some other place on the Continent. The most unpleasant aspect of British weather is fog and smog. This is extremely bad in big cities and especially in London. The fog spreads everywhere, it is in the streets and it creeps into the houses. Cars move along slowly, but still street accidents are frequent in the fog. People cannot see each other. They creep along the houses touching them with their hands not to lose their way or not to be run over by a car. Questions 1. Is the weather in England very chageable? 2. How often does it rain in England? 3. What do Englishmen often say to describe the weather of their country? 4. Englishmen often talk about weather. Do you find this topic of conversation interesting? 5. What is the worst time of the year in England? 6. When do Englishmen prefer to stay at home by the big fire? 7. How do te English spend their short English summer? 8. What are London smogs? 9.What king of weather do you lik best of all ? 10. Which do you like better: when its cold or hot? 11. What is the weather like today? 12. What is the weather forecast for tomorrow? 12. What is the weather lik in your town in winter (summer, autumn, spring)?