по теореме Фалеса прямые проведеные через середину третьей стороны параллельные данным сторонам(прямым содержащим стороны) пройдут через середины этих сторон, т.е. поделят стороны а и b пополамА значит полученные отрезки будут средними линиями треугольниками. По свойству средней линии треугольника их длины будут равны половинам соотвествующих сторон, т.е. a/2 и b/2.Две другие стороны четырехугольника равны половинам соотвествующих сторон треугольника, т.е. a/2 и b/2.Периметр четырехугольника сумма длин всех его сторонпоэтому периметр полученного четырехугольника равенa/2+a/2+b/2+b/2=a+bответ: a+b
Friendship is very important in our life. Let me explain you why I think so. Everybody needs someone who is close to your heart and way of thinking. Your parents will always love you anyway because they are parents. And your friend just likes you; he wants to spend his time with you and he is willing to help you when you need it.My best friend’s name is Stepan. He is not my schoolmate. Stepan lives next to me and our parents are good friends. We first met on my mom’s birthday party three years ago. Since then we see each other almost every day.Stepan is one year older. He is fond of tennis very much. He plays tennis since childhood and he even won some tournaments. Maybe once he will become a professional player. Stepan is very clever, honest and friendly. He likes to read books and watch films, that’s why it’s always interesting to talk to him. We usually discuss our favorite characters and most exciting actions. Also we both like to ride the bicycle and to listen to music so we are never bored together. I think it’s very important to have common hobbies with a friend.I’m sure that we both are willing to help each other in need. Stepan usually explains me mathematics when I don’t understand something. He visits me when I’m ill. He never envies me. I know that I can trust my best friend. As for me, I also try to do my best to be a good friend for him too. I’m happy to have such a good friend.
