# I like Pi

1. May 8, 2006

### Universe_Man

Pi is the most interesting number. I was thinking about the value for Pi that is accepted by the Scientific and Mathematic community, which starts off as 3.141592653... and so on to infinity.

My question is, How did they get this value of Pi as the most approximate? Did they use extremely fine implements of measuring, or is there a clever mathematical way of finding what the exact decimal values are out to a certain number of places? I don't know. Also, since pi goes on into infinity, does that mean that the circumference of a circle has no exact value?

2. May 8, 2006

### Jameson

Check out this Wikipedia page on the history of Pi. There are many, many methods of calculating it to billions of digits. http://en.wikipedia.org/wiki/Pi

3. May 8, 2006

### Hurkyl

Staff Emeritus
No. It merely means that the circumference of a circle of diameter 1 cannot be written exactly as a terminating decimal number. Its exact value is pi.

4. May 13, 2006

### rcgldr

5. May 13, 2006

### Gokul43201

Staff Emeritus
If you believe that the circumference has no exact value because it is a diameter times pi, then you should also believe that the diameter (or twice the radius) has no exact value, since that is just the circumference over pi (and 1/pi also has a non-terminating decimal representation). But the radius is just the distance between the center and a point on the circle. From this you must conclude that the distance between two points has no definite value. Virtually all of geometry then becomes meaningless.

All these problems are overcome by replacing your incorrect notion about pi with the statement in Hurkyl's post.

Last edited: May 13, 2006
6. May 14, 2006

### rcgldr

He was asking a question, not stating a belief or notion.

To answer the question, the conventional methods used to decribe numbers have a weakness for radicals (like square root of 2) or transcendental (like pi) numbers, as these values can't be represented as a fixed point number with a finite number of digits, or as a fraction with a finite number of digits. So in the math world, they are just written as symbols, like pi, or descibed with mathematical terms, like square root of 2, or 4 times the inverse tangent of 1.

In the case of standard geometry, it's not possible to create a straight line that is pi times longer than another line.

On a number line, every real value is a (infinitely small) point on the line. With this analogy, pi is an exact point on the number line, as well as the square root of 2, or a simple integer like 1. There's no issue with these values on the number line, the issues occur when we try to come up with a means to describe values using fixed point number or fractions.

Last edited: May 14, 2006
7. May 14, 2006

### rhj23

is there such a thing as a point on a line that is not infinitely small?

8. May 14, 2006

### Gokul43201

Staff Emeritus
Point noted. Sorry for the misrepresentation.

9. May 14, 2006

### rcgldr

No, which is why I put it in paranthesis for those few readers that may not understand the point about points. (almost sorry for the bad pun).

10. May 14, 2006

### rcgldr

Other than e and pi, are there any other common transcendentals?

11. May 14, 2006

### Curious3141

Liouville's constant $$L = \sum_{n=0}^{\infty} {10^{-n!}} = 0.1100010...$$ has '1's in every decimal place that's a factorial, and zeros elsewhere. It's the first number to be proven to be transcendental.

Champernowne's number, formed by concatenating decimal representations of the naturals. $$0.123456789101112...$$, proven to be transcendental.

$$e^{\pi}$$ known to be transcendental, can be easily proven with Gelfond's theorem. $${\pi}^e$$ is suspected but not known to be transcendental.

$$2^{\sqrt{2}}$$, Hilbert's number, known to be transcendental, provable by Gelfond's theorem.

There are many other numbers that are suspected but not known to be transcendental, e.g. $$\zeta(3)$$, Feigenbaum's constant, Catalan's constant, etc.