Pi By Tracy Hanzal

What is Pi? Pi is the ratio of circumference of a circle to diameter of a circle The symbol for pi Circumference diameter = Circumference Diameter

The Value of pi In all circles, the ratio of circumference to diameter results in the same value: Approximate value: = 3.14159265359……… Pi is an infinite decimal with no pattern in the decimal value. Pi may be used to find the circumference of a circle if the diameter is known or to find the diameter if the circumference is known or also to find the area of a circle. Pi is also used in trigonometry in measuring the radians in a coordinate plane. When approximating the circumference or area of a circle, the value of 3.14 is most commonly used and another value commonly used is the fraction 22/7.

History of Pi There is evidence that the ancient Egyptians and Babylonians were aware of a common value in circles. The Egyptians figured a value for pi to be 4 x (8/9)2, which is about 3.16045. This value is not very accurate and difficult to work with. The Babylonians had an easier number to work with. Records show that their value for pi is 3 1/8, which is 3.125. Both civilizations approximations of pi are obviously not as accurate as the value we have today, but they knew there was a common ratio and they knew that the value was a little more than three.

Computation of pi from 2000 B.C. More History of Pi Computation of pi from 2000 B.C. Who Year Value for pi Babylonians 2000 BCE 3.125 Egyptians 3.16045 China 1200 BCE 3 Bible (1 Kings 7:23) 550 BCE Archimedes 250 BCE 3.1418 Ptolemy 150 AD 3.14166 Fibonacci 1220 AD 3.141818

Symbol for pi Introduced by William Jones in 1706 The Greek Letter Pi was chosen to represent the value 3.14159….. The Greek letter, shown at the write is pronounced like our letter “p” which stands for perimeter.

Examples Diameter = 6 cm AREA OF CIRCLE = r2 Find the area of the circle: A = pi x r2 A ≈ 3.14 x (3 cm)2 A ≈ 3.14 x (9 cm2) A ≈ 28.26 cm2

Examples Volume of a Cone: h = 10 cm V ≈ 3.14 x (4 cm)2 x (10 / 3 cm) V ≈ 167.467 cm3 r = 4 cm

Works Cited http://www.ualr.edu/~lasmoller/pi.html http://math.forum.org/dr.math/faq/faq.pi.html http://www.cecm.sfu.ca/project/ISC/Pihistory.html http://www.equationsheet.com/eqninfo/Equation-73.html