By far the most popular and well-stocked category of used instruments is our selection of guitars, where we've got a huge variety of all the big names. Used Gibson Les Paul, pre-owned Fender Telecaster and secondhand Stratocaster guitars are commonly found within these pages, waiting for their new homes with players and collectors.
22/7 is a pretty decent choice for teaching 11-year-olds about fractions that are close to pi. 355/113 would be better, if you think they can remember numbers that big. And approxRational is fun. Exercise for the interested reader: implement an inverse to approxRational.
By definition, pi is the ratio of the circumference of a circle to its diameter. Pi is always the same number, no matter which circle you use to compute it. For the sake of usefulness people often need to approximate pi. For many purposes you can use 3.14159, which is really pretty good, but if you want a better approximation you can use a computer to get it. Here's pi to many more digits: 3.14159265358979323846. The area of a circle is pi times the square of the length of the radius, or pi r squared: The modern symbol for pi [] was first used in our modern sense in 1706 by William Jones, who wrote: Pi (rather than some other Greek letter like Alpha or Omega) was chosen as the letter to represent the number 3.141592...