Втреугольной пирамиде sabc площадь основания abc равна 7, а углы abc,
asb и двугранный угол при ребре ab равны п/2. рассматриваются проекции
пирамиды sabc на всевозможные плоскости, проходящие через прямую ав.
наибольшая из площадей таких проекций равна 14, а наименьшая площадь рана
4 корень из 3. найти объем пирамиды.
- Tom, would you like to join one of the youth movements?
- For example?
- What do you think about "The Green Movement"?
- Well, maybe. I like nature. What about you?
- Me too. I'm sure that it cannot protect itself from such a greedy species as human beings. It needs help.
- Absolutelly agree with you.
- What about another movement? It is called "Young people for Peace"
- Nice name and great goals it has, I guess. Every sensible person on the Earth wants to live in peace. Me too.
- That's right. I've heard about one more movement - The Stay Healthy Monement.
-Oh, souds great. I'd like to to take part in it. I'm for healthy life. I'm really against smoking, drinking, drugs and so on.
- I think I'll join this movenemt. Are you with me?
- I'll think.
- ok. They have a meeting tomorrow at 6 pm. I'm going. We could come together.
- I'll call you tomorrow after a considerate thought about it. Talk to you tomorrow. I need to go now.
- Bye, till tomorrow.
A hobby is a favourite pastime of a person. Hobbies differ like tastes. If you have chosen a hobby to your liking, lucky you are: you have made your life more interesting.
Numerous hobbies can be subdivided into four large classes: doing things, making things, collecting things, and learning things.
The most popular of all hobby groups is doing things. It includes a wide variety of activities, everything from gardening to travelling and from chess to volleyball. Gardening is one of the oldest man’s hobbies, especially in some countries (Britain, for example). A relatively new hobby which is becoming more popular is computer games.
Making things includes drawing, painting, making sculpture, designing costumes, and handicrafts. Some hobbyists write music. Two of the most famous hobby painters were President Eisenhower and Sir Winston Churchill.
Almost everyone collects something at some period in his life: stamps, coins, matchboxes, books, records, postcards,, toys, watches. Some collections have no real value. Others become so large and so valuable that they are housed in museums and galleries. Many world-famous collections started in a small way with one or two items. People with a good deal of money often collect paintings, rare books and other art objects. Often such private collections are given to museums, libraries and public galleries so that others might take pleasure in seeing them.
No matter what kind of hobby a person has, he always has the opportunity of learning from it. By reading about the things he is interested in, he is adding to what he knows. Learning things can be the most exciting aspect of a hobby.