How many digits of pi did you memorize?

[Saint Nick]

3.14159

 

[Matthiasa]

The problem with education in America:

Everyone can recite pi to x digits.

Almost no one can give a geometric proof of A = pi r.

Well then good thing it's A=pi*r^2 then.

 

[Farmer]

Well then good thing it's A=pi*r^2 then.

Doh! I meant C = 2 pi r

You see what I mean?!

 

[OverVolt]

Doh! I meant C = 2 pi r

You see what I mean?!

They don't teach it anymore. The fundamentals are not taught. I never understood how a cars differential worked until I saw some 1950's video that actually had a really awesome presentation. Alot of the scholars today learned the fundamentals from the ground up and then they teach you the modern day ideas derived from those fundamentals and no one actually understands how we got there. The "how we got there" is also memorized lulz.

 

[Matthiasa]

The good/easy proofs for that involve calculus though, which given most peoples math ability is kind of pushing it.

 

[WHAMPOM]

10 for me

3.141592654

You need to know this important constant to rebuild earth when we get hit by an asteroid in the not so distant future!

For most things rounding it off to 3.0 works OK.

 

[mnewsham]

They don't teach it anymore. The fundamentals are not taught. I never understood how a cars differential worked until I saw some 1950's video that actually had a really awesome presentation. Alot of the scholars today learned the fundamentals from the ground up and then they teach you the modern day ideas derived from those fundamentals and no one actually understands how we got there. The "how we got there" is also memorized lulz.

http://www.youtube.com/watch?v=K4JhruinbWc

 

[DrPizza]

That's a little less than .0000269% off

I'm OK with that; it's only about a mile off when calculating the circumference of the earth.

Since this is a mathematical thread, I suppose we should correct bad math skills in the thread. It actually works out to a little less than 0.0000844664% error, which is 3.14 times larger.

As pointed out though, the diameter of the Earth varies, depending on which way you go. For instance, from North Pole to South pole, the diameter is approximately 7901 miles. But, at the equator, it bulges out a bit, giving a diameter of approximately 25 miles more. Nonetheless, using this rounded value of pi to find the circumference at the equator (assuming a smooth surface) only results in an error of 0.021 miles, or, 111 feet.

22/7

For more accuracy you can increase that. 44/14 or 110/35 etc.

Hmm whats a good calculation for accurate pi? I noticed its way off like dixy said.

I hope that's sarcasm, because 22/7 and 44/14 are the same thing.
The best rational approximation with fewer than four digits in the numerator and denominator is 355/113. It's accurate to six decimal places. The next better rational approximation has 5 digits in each the numerator and denominator, and is still only accurate to 6 decimal places.

It's easy to remember that approximation...
113355. Last 3 digits divided by the first three.

 

[OverVolt]

It wasn't sarcasm lulz. I used to have a method and didn't bother to check what it was lmao. Side effect of not being afraid to be a dumbass in front of people anymore. You learn more that way. Its a tactic =]

Shame on everyone who missed it lmao. But I did something similar to what you just did.

 

[Joseph F]

3.141

 

[Matthiasa]

It wasn't sarcasm lulz. I used to have a method and didn't bother to check what it was lmao. Side effect of not being afraid to be a dumbass in front of people anymore. You learn more that way. Its a tactic =]

Shame on everyone who missed it lmao. But I did something similar to what you just did.

22/7 and 110/35 are also the same thing since you now care about it.

 

[Powermoloch]

pie is 3

 

[DrPizza]

Doh! I meant C = 2 pi r

You see what I mean?!

Are you sure that's what you meant, and not the area formula? Because the above formula is pretty trivial to prove. Here, I'll show you:

Pi is the ratio of a circle's circumference to its diameter. BY DEFINITION
So, pi = C/D
And, the diameter is twice the radius, so
Pi = C/(2r)

Multiply both sides by 2r (multiplicative property of equality), 2r's cancel out on the right side (multiplicative inverse, and multiplicative identity)
2 pi r = C
QED

 

[alkemyst]

all of them.

 

[thecrecarc]

Are you sure that's what you meant, and not the area formula? Because the above formula is pretty trivial to prove. Here, I'll show you:

Pi is the ratio of a circle's circumference to its diameter. BY DEFINITION
So, pi = C/D
And, the diameter is twice the radius, so
Pi = C/(2r)

Multiply both sides by 2r (multiplicative property of equality), 2r's cancel out on the right side (multiplicative inverse, and multiplicative identity)
2 pi r = C
QED

I'm curious, what would be a proof of A=pi*r^2? The easiest thing I can think of is integrating from 0 to radius of 2*pi*x dx. But that one can hardly expect everyone to learn calculus to do that proof....

 

[Farmer]

Are you sure that's what you meant, and not the area formula? Because the above formula is pretty trivial to prove. Here, I'll show you:

Pi is the ratio of a circle's circumference to its diameter. BY DEFINITION
So, pi = C/D
And, the diameter is twice the radius, so
Pi = C/(2r)

Multiply both sides by 2r (multiplicative property of equality), 2r's cancel out on the right side (multiplicative inverse, and multiplicative identity)
2 pi r = C
QED

Um, yes, but the numerical value of pi at 3.14... is what I am asking for the proof of. It is not trivial. Don't be a smartass.

thecrecarc:

You do not need calculus to prove A = pi r^2, as I'm sure it was known before Newton's time. The harder proofs are all geometric. I really wouldn't consider a calculus based proof a proof, since it is trivial in calculus. There are also non-calculus proofs, like those with inscribed polygons, which essentially amount to calculus proofs.

However, schoolkids (including myself) were simply told A = pi r^2, C = pi 2r, pi = 3.14..., without proof. Not knowing any better, we instead spend our efforts memorizing pi to some number of digits.

 

[Kev]

22/7

For more accuracy you can increase that. 44/14 or 110/35 etc.

wat

 

[shortylickens]

3.2.

If I need the rest its on my calculator.
You'd be amazed how much I dont need it in calculus.

 

[Veliko]

I don't know what you mean.

Pi is a set number that me and my supermodel girlfriend can remember easily.

 

[TheNinja]

Before this thread

3.14

After this thread

3.14159 - Doubled my knowledge!!

 

[shortylickens]

Also I hate when people tell me to use 22/7 cuz its WAY off from that. You'd do better to just use 3.14 if you arent gonna be exact.


0.00126448926734961868021375957764
Thats the difference. If you are doing something that actually matters and needs accuracy, you should not be using 3 & 1/7th.

 

[mnewsham]

Before this thread

3.14

After this thread

3.14159 - Doubled my knowledge!!

3.141592653589793238462643383279

():awe:

 

[DrPizza]

Geometrically, by hand, you're not getting very far in establishing the value to very many decimal places. Inscribing a hexagon in a circle indicates that the circumference is more than 6 times the radius, so a little more than 3. But to get more than three correct significant digits, you need more than 100 sides in your polygon. (at least with the method I'm most familiar with.) Nonetheless, I fail to see how a geometric only method is going to produce more than a few digits of pi, let alone "prove the value" without the aid of a computer or calculus. Remember, it was a couple thousand years before more than the first ten digits were known.

 

[Saint Nick]

AFTER THE BURIAL - Pi
www.youtube.com/watch?v=io8mnNVsaqE

 

[DrPizza]

As for a demonstration for the area formula (this'll be hard without a picture to show.)

Picture a pizza cut into 8 pieces. (of course I would use pizza to "prove" the area formula)
Line up 4 slices side by side pointing forward. Line up the other 4 slices in front of these pointing toward you. Mesh them together, you get something roughly in a rectangular (or, closer to the shape of a parallelogram), except the side closest to you and farthest from you would be curvy from the arcs of crust.

Repeat this, except cut the pizza into 16 slices. Now, it's closer to the shape of a parallelogram, though the angles in the corners are closer to 90 degrees. Now, imagine doing this with a pizza cut into 100 slices... 1,000,000 slices... It gets closer and closer to the shape of a rectangle. The height is obviously getting closer to the radius of the circle, and the length is getting closer and closer to a straight line with a length of half the circumference. Area = length times width = 1/2 * 2 pi r * r.
Though, this really doesn't constitute "proof."