В основании пирамиды лежит равнобедренный треугольник, боковая сторона которого равна а, а угол при основании равен а. Боковые грани

Big Ben
Perhaps even small children know what a Big Ben is. Firstly, it’s the symbol of Great Britain and one of the most beautiful sights of London. Secondly, it’s the largest and the most famous clock in the world. Originally, Big Ben is a tower. It’s one of the highest towers of Westminster Palace. Officially, the clock has started its work on 31 May 1859. According to one of the theories the clock has been named Big Ben after Sir Benjamin Hall, who directed work on the casting of the bell. Another theory claims that it has been named after Benjamin Caunt, who was one of the well-known heavyweight boxers of the 19th century. Surprisingly, the tower of Big Ben used to be a prison where over riotous parliamentarians were kept. Big Ben has become a popular souvenir for tourists. Almost all visitors of London buy a small souvenir in the shape of the world-famous clock. Also Big Ben can be often seen in famous films and ads. Official name of the tower is the “Westminster Palace Clock Tower” or “St. Stephen's Tower”. Big Ben is only the name of the clock itself along with the bell. The history of Big Ben dates back to 1288, when it was built for the first time on Ralph De Hengham’s money. He was the chairman of the Supreme Court of Queen's Bench. However, the contemporary tower of Big Ben was built according to Charles Barry’s project in the 19th century, as the old building was destroyed due to the fire of 1834. Although Big Ben is very popular with spectators, no one is allowed inside of the tower. All the Londoners who live close to Big Ben can hear how the bell strikes thirteen at New Year’s Night.