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Dr. Math FAQ:
Pi = 3.14159...
3D and higher
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- Accuracy in Measurement [02/08/2002]
Since pi is irrational, either the circumference or the diameter of a
circle must be irrational. How is that possible?
- Calculating Pi - Brent-Salamin Algorithm [05/11/2000]
Can you show me a simple method to calculate pi accurately to an
arbitrary number of digits?
- Facts about Pi [03/09/1997]
What are some interesting facts about pi?
- Finding Pi: Buffon's Needle Method [1/31/1996]
I was hoping to find a surprising way of finding pi using a needle and
- Formula for Pi [6/28/1995]
I would like to know the formula for Pi that was used to calculate out to
the bazillionth digit for the memory contests.
- Pi and the Area of Circles [05/11/1997]
If pi truly goes on and on forever without repeating, is it impossible to
find the exact area of a circle?
- Pi is a Constant [4/22/1995]
A couple of weeks ago I got the first 21500 digits of PI by
Infobot@Infomania.com. As an example for internet-capabilities I showed
it to some friends. One of them told me the exact result of PI depends
on the extent of the circle diameter. This can't possibly be right, can
it? And are there different ways of calculating PI?
- Questions about Pi [12/5/1995]
Why does pi repeat so much, and can you write it out for me?
- Radius of a Pizza [8/27/1996]
If a pizza has an area of 30 inches, what is its radius?
- Teaching Pi [03/04/1997]
How can I teach my students where 3.141592... comes from and then let
them experiment with it?
- Two Unusual Ways of Estimating Pi [03/24/1997]
I'm looking for two unusual ways of getting pi that don't have anything
to do with circles or spheres.
- What is Pi? [03/02/1997]
Is it a number, an equation, or what?
- What is the Value of Pi? [6/19/1995]
What is the value of pi? What is the square root of pi?
- Why is Pi a Constant? [08/01/2000]
Why is the circumference of a circle divided by the diameter, or pi, the
same number for every circle?
- Why Pi? [01/25/2001]
Why do we use pi when we calculate the circumference and area of a
- 2000 Decimals of Pi [6/8/1995]
What are the first 2000 decimals of pi?
- Activities to Find Pi [10/07/1998]
Can you suggest any classroom activities to find pi, other than the
standard way of measuring the circumferences and diameters of circles?
- Alabama legislature and pi [04/15/1998]
Did Alabama really vote that pi should have its biblical value of 3?
- Algorithm for Finding Pi, in C [02/14/1998]
I would like to know how to implement various algorithms for finding pi
in the C language.
- Approximating Pi using Geometry [08/12/1998]
I need to know a simple method to find the approximate value of pi using
- Archimedes' Method of Estimating Pi [5/29/1996]
What was Archimedes' method for estimating pi using inscribed and
circumscribed polygons about a circle?
- Are All Digit Strings in Pi? [08/06/1999]
Do all possible digit combinations appear in pi? For example, is it
possible that somewhere in the decimal expansion there are a million 2's
in a row?
- Buffon's Needle: a Proof [08/13/1997]
I have known the Buffon's needle problem for the last 28 years and have
yet to come across its theoretical proof.
- CADAEIBFEC and Other NCTM Questions [10/27/1998]
CADAEIBFEC is a mnemonic for an important piece of mathematical
information. What is it?
- Calculating Any Digit of Pi [05/16/2000]
Is there a formula that gives any digit of pi without calculating the
- Calculating Pi - the Nail Drop Experiment [05/19/1999]
Do you have any information about calculating pi by means of the nail
- The Circumference of a Circle [11/4/1995]
- Contradiction in definition of pi? [08/09/1997]
How can circumference (a finite, rational number) divided by diameter a
finite, rational number) give a number that is irrational?
- Count Buffon's Needle [05/21/1997]
Draw a series of parallel lines a distance d apart on a piece of paper.
Drop a stick of length l on the paper n times. If the stick crosses a
line s times, the value of pi can be found from the equation s/n =
2*l/pi*d. Where does this equation come from?
- Deriving Pi [05/10/2001]
I know that Pi is equivalent to 3.14, but what formulas are used to come
up with 3.14?
- Determining the Value of Pi [8/5/1996]
Is Pi the circumference of a circle divided by the radius?
- Digits of Pi [6/14/1996]
How many digits of the ratio "pi" have we figured out, and what are they?
Is it endless? How did people figure it out?
- Does Pi Equal 3.14? [01/27/1998]
We use pi as 3.14. How can this be right?
- Egyptian Equivalent of Pi [05/15/2003]
The ancient Egyptians used the formula (d-d/9)^2 for the area of a
circle with diameter d. What value for pi does the formula yield?
- Einstein, Curved Space, and Pi [10/09/1999]
If space is curved and Euclidean geometry doesn't apply, doesn't that
mean that the value of pi changes and can sometimes be rational?
- Explorations of the Circle [02/09/1999]
What is the definition of a circle? How does it relate to pi? What are
the important parts of a circle?
- Finding a Circle's Area Without Pi [02/24/2001]
How can I find the area of a circle without using pi?
- Finding Pi [11/14/1997]
What is the quickest algorithm for finding pi?
- Finding Pi [2/8/1996]
Why is pi 3.14?
- Formulas Regarding Radio Waves [11/17/2004]
Why does 2pi appear in many formulas involving high frequency radio
transmissions and antennas?