Diamond M.

asked • 12/19/14

Can you explain the term PI (sorry dont have the symbol) for me? Please and Thank You

My teacher has explained this to me millions of times. I still don't get it. Makes no sense. I wanna know what it equals, how you get it, how/when you use it, Ect...... Thanks

2 Answers By Expert Tutors

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Matt H. answered • 12/20/14

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5.0 (335)

PATIENT :-) Elem/Middle MATH and WRITING; HS SAT and COLLEGE ESSAYS!

Dawid S. answered • 12/19/14

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5.0 (21)

ACT/SAT Math and Algebra Tutor

Dawid S.

The number pi is simply an artifact, it's not rational. It's literally defined as the ratio of the circumference of a circle to its diameter.
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12/19/14

Bill P.

No, he did not "figure out" that pi = r^2, rather the Area = pi multiplied by the square of the radius.
If a circle has a radius of length r, then its circumference = pi multiplied by twice the radius. When you take a calculus course you should discover that the circumference of a circle is the first derivative of the area with respect to the radius. Also, you should learn that the surface area of a sphere id the first derivative of the volume with respect to the radius. Think of the Volume as a function of the radius. Now, v = f(r) = 4/3 times pi times the cube of r, where r is the radius. Now dV/dr = 3 times 4/3 times pi times the square of r which simplifies to 4 times pi times r^2.
 
 
BTW, if your calculator does not have a special key for "pi" please use 355/113 which calculators will display as 3.14159292... which is a very good approximation since "pi" is actually 3.14159265... only off by approximately 27 units out of 100,000,000 (100 million). 
 
 
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12/19/14

Dawid S.

It doesn't make sense in our base-10 number system, it's one of many irrational numbers we rely on frequently. It's just irrational because it is, we can't change the way nature is. 
Getting deep into it you could make a base-pi numbering system and it could be the base unit, then pi would be the rational number :P
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12/19/14

Dawid S.

I meant A=pi r2 not sure how I missed that. Wrote that answer late at night.
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12/24/14

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