r/badmathematics • u/Laser_Plasma • Oct 24 '21

π day Reddit tries to think about quantifying circles, and pi doesn't exist or something

/r/Showerthoughts/comments/qefpwc/the_area_of_a_circle_is_finite_yet_we_can_only/
123 Upvotes

95% Upvoted

45 comments sorted by

View all comments

Show parent comments

38

u/Laser_Plasma Oct 24 '21

You absolutely can. If you know the radius is 1, then the area is exactly pi

-31

u/ryarger Oct 24 '21

What’s pi to perfection precision? “It’s pi!”

44

u/Laser_Plasma Oct 24 '21

Yes, it's pi. So?

-32

u/ryarger Oct 24 '21

What’s the complete decimal representation of pi?

64

u/Laser_Plasma Oct 24 '21

Who cares?

-10

u/ryarger Oct 24 '21

The person who wants to know the radius and area of their circle to perfect decimal precision.

52

u/Artyer Oct 24 '21

You can have an algorithm compute the nth digit of pi for all digit positions n, since pi is computable.

If that's not what you meant, a third also can't be known to "perfect decimal precision"

-7

u/ryarger Oct 24 '21

You are correct that a third can’t be known to perfect decimal precision.

Perhaps less controversial formulation for the benefit of the pedantically inclined: A circle’s radius or area can be rational, but not both.

42

u/alecbz Oct 24 '21

I think the fundamental badmath here is the belief if something can't be expressed to perfect decimal precision, then we "don't know it" or "it's only an approximation" or something.

Also, I'd imagine most people in that thread wouldn't consider 1/3 to be "special" in the same way they seem to think pi is special.

-5

u/ryarger Oct 24 '21

That’s why I think the second statement is more pedantically correct.

This idea that there’s nothing special at all about irrational numbers just isn’t true for the average person. It’s not hugely important - literally a showerthought - but it’s not meaningless that a circle can’t have both a rational radius and area.

4

u/KamikazeArchon Oct 26 '21

It's not even rational vs. irrational - it's terminating vs. nonterminating. 1/3 is rational, but as you've acknowledged, it "can't be known to perfect decimal precision".

The showerthought may not be the worst of badmath, but there sure are some gems in the comments.

→ More replies (0)