Each year on March 14, many mathematicians hold festivities for 'Pi Day'. The date corresponds with the first three digits of the number (3.14). In the United States, some teachers bake pies at home and take them to school on Pi Day. To get a slice, students have to do calculations involving pi. Students may be asked to find out the circumference of the pie, or the size of each slice so that eight students can share the pie equally. Sometimes teachers set questions on the concept of pi itself. For example, how do you find its value? How many digits does it have when expressed as a decimal number. What is it for? Let's see what pi really is. By definition pi is the constant ratio of the circumference of a circle to its diameter. It is not known who discovered pi. However, one thing is certain, the constant has a long history. Ancient Egyptians knew about its existence. So did the Greeks, Hebrews and Babylonians. The earliest known reference to pi is found on a papyrus scroll from the Middle Kingdom period in ancient Egypt. It was written around 1650 BC. The end of the scroll poses some mathematical problems and a rough figure for pi was applied in the calculation of a circle's area. The symbol pi is a letter from the Greek alphabet. The letter was chosen and first used in the 18th century because it was pronounced like 'p' for perimeter. Pi is an infinite decimal number. In other words, it has an infinite number of figures to the right of the decimal point. However, for practical purposes, people used to round off pi to 3.1416 before the widespread use of computers. The practical applications of pi are everywhere. Here are some examples: How much drink can your glass hold? How many sprinklers does your school need to water the garden outside your classroom? How much fuel does an aeroplane need for a flight between Hong Kong and the United Kingdom. Remember, when planes fly around the globe, they are actually travelling on the arc of a circle. Send your questions and comments about English Corner to Agatha Ngai, agatha@scmp.com Graphic: 1403P4GYO
