# Questioning of pi

1. Jan 15, 2015

### Mr.maniac

here's my question:

which is right:

3.14159265359 blah blah blah
-supported by http://www.quora.com/Why-is-PI-22-7 [Broken]
also says that 22/7 is an approximation

or

22/7 which is 3.14285714286(I don't know extended or not.)
-supported by my maths teacher
-supported by my fat ol' friend

Last edited by a moderator: May 7, 2017
2. Jan 15, 2015

### Staff: Mentor

-supported by mathematics, which is the only thing that really counts.

Which is not a very good approximation, as you can see compared to the value you wrote above.

Last edited by a moderator: May 7, 2017
3. Jan 15, 2015

### Borg

PI isn't here but like these, 22 / 7 is just an approximation.
Source: http://xkcd.com/1047/

4. Jan 15, 2015

### Mentallic

If your teacher thinks that pi is exactly equal to 22/7, then I'm worried for your class.

Google is correct. Pi is approximately equal to 22/7, but not exactly equal.

5. Jan 15, 2015

### Borg

Here's a better approximation for PI - 355 / 113. It's good to 6 decimal places but like 22 / 7, it isn't exactly equal to PI.

6. Jan 15, 2015

### Mr.maniac

She says that 22/7 is the correct value of pi and 3.141 blah blah is just an approximation.

7. Jan 15, 2015

### Borg

Wow. I'm with Mentallic on this. Sorry for your class if that's what she is teaching.

8. Jan 15, 2015

### Mr.maniac

Then shall I conclude that my maths teacher is wrong along eith my fatso friend.

9. Jan 15, 2015

### Mr.maniac

Alsi it wasn't taught a simple algaebric expression was given to break down which was
3.14r
As I like pi strarted all about pi and my friend calculated 22/7 and then a debate then asking the teacher (asking for a fez).

10. Jan 15, 2015

### Borg

The problem is that she is teaching this to people. It would be great if you could get her to create an account and post her logic here. There would be plenty of people who would be happy to explain it to her. :)

11. Jan 15, 2015

### PeroK

Here's an interesting take on this:

$\pi = \frac{22}{7} - \int_{0}^{1} \frac{x^4(1-x)^4}{1+x^2} dx$

12. Jan 15, 2015

### Quantum Defect

13. Jan 15, 2015

### HallsofIvy

Since your teacher is not here to defend him- or her-self, did he or she say that "pi is equal to 22/7" or "It is better to use 22/7 for pi than 3.14"?

14. Jan 15, 2015

### Mr.maniac

Let me quote my teacher :

"22/7 is the exact value of pi and 3.141 is an approximation"
(I'm I getting her wrong")

15. Jan 15, 2015

### DrewD

She is right about the second part, but the first is also an approximation.

Mr.maniac, I don't know you so please don't be offended by what I say/ask: Is that actually an exact quote or is that what you think you remember from the middle of an argument. I only ask this because I teach, and while I have definitely misspoken, I am more often misquoted.

Is it possible that this is on a standardized test that explicitly told you to use the value 3.14 or 22/7 for $\pi$ in your calculations? If this is the case, you may have misunderstood her telling you to use that value. If there wasn't some strange context (eg. she preceded it by saying, "the next statement I make is false" ), she was wrong.

Also, in these sorts of debates (math debates) wikipedia is usually pretty reliable.

16. Jan 15, 2015

### Staff: Mentor

22/7 $\approx$ 3.142857. Both 22/7 and 3.141 are approximations to the actual value of $\pi$. According to wikipedia, the first 50 digits of $\pi$ are 3.14159265358979323846264338327950288419716939937510 (http://en.wikipedia.org/wiki/Pi). Clearly 3.141 is a better approximation than 22/7.
???
Are you trying to say "Am I getting her wrong?"

17. Jan 16, 2015

### Mr.maniac

(Yes it's am I getting her wrong)
And DrewD they are the exact words of my teacher.

18. Jan 16, 2015

### Mr.maniac

And she is saying 3.141 blah blah is wrong

19. Jan 16, 2015

### DaveC426913

Please see Mark44's post #16 above.
22/7 AND 3.1416 are both approximations. He has listed the correct value of Pi to 50 digits.

If your teacher is saying anything otherwise, she is wrong.

20. Jan 16, 2015

### DrewD

Well that's unfortunate. I would nicely do what she wants in class but carefully check to be sure it is correct. If it is incorrect, ask her and if she doesn't realize the mistake, keep track of it and let an administrator know. Well, that's not actually what I would have done, but it is the most likely way to actually accomplish something.

21. Jan 16, 2015

### Khashishi

Your teacher is teaching you a very good lesson here. Don't believe everything your teacher says.

22. Jan 17, 2015

### pwsnafu

Very much so. In year 7, I had a teacher that claimed that the orbits of the planets were perfect circles. When another student questioned him he said "That's just how they draw it".
Mr.maniac, do you think it's possible if you can get your teacher to create an account here? Or as Drew said, talk to an administrator. The problem is that this teacher will continue to teach in the future, and it means all future students will be taught incorrectly.

23. Jan 17, 2015

### Mr.maniac

Well said Khashishi

24. Jan 17, 2015

### Mr.maniac

Well not possible to make her make a account here but will try to convince her.
(By the way how to close a thread cause will close this one after she is convinced)

25. Jan 17, 2015

### phinds

You cannot close threads, only moderators can do that. If you really feel the need to close a thread you can hit the "report" button and ask for it to be closed, but whether or not it IS closed is up to the moderators.