I’d just say that not all fractions can be broken down into a proper decimal for a whole number, just like pie never actually ends. We just stop and say it’s close enough to not be important. Need to know about a circle on your whiteboard? 3.14 is accurate enough. Need the entire observable universe measured to within a single atoms worth of accuracy? It only takes 39 digits after the 3.
Pi isn’t a fraction – it’s an irrational number, i.e. a number with no fractional form in integer bases; as opposed to rational numbers, which are defined as being able to be expressed as a ratio of two integers (a fraction). Furthermore, π a transcendental number, meaning it’s never a solution to f(x) = 0, where f(x) is a non-zero finite-degree polynomial expression with rational coefficients. That’s like, literally part of the definition. They cannot be compared to rational numbers like fractions.
Since |r|<1 => ∑[n=1, ∞] arⁿ = ar/(1-r), and 0.999... is that sum with a = 9 and r = 1/10 (visually, 0.999... = 9(0.1) + 9(0.01) + 9(0.001) + ...), it’s easy to see after plugging in, 0.999...=9(1/10) / (1-1/10) = 0.9/0.9=1). This was a proof present in Euler’s Elements of Algebra.
The problem is, that’s exactly what the … is for. It is a little weird to our heads, granted, but it does allow the conversion. 0.33 is not the same thing as 0.333… The first is close to one third. The second one is one third. It’s how we express things as a decimal that don’t cleanly map to base ten. It may look funky, but it works.
Somehow I have the feeling that this is not going to convince people who think that 0.9999… /= 1, but only make them madder.
Personally I like to point to the difference, or rather non-difference, between 0.333… and ⅓, then ask them what multiplying each by 3 is.
I’d just say that not all fractions can be broken down into a proper decimal for a whole number, just like pie never actually ends. We just stop and say it’s close enough to not be important. Need to know about a circle on your whiteboard? 3.14 is accurate enough. Need the entire observable universe measured to within a single atoms worth of accuracy? It only takes 39 digits after the 3.
Pi isn’t a fraction – it’s an irrational number, i.e. a number with no fractional form in integer bases; as opposed to rational numbers, which are defined as being able to be expressed as a ratio of two integers (a fraction). Furthermore, π a transcendental number, meaning it’s never a solution to
f(x) = 0, wheref(x)is a non-zero finite-degree polynomial expression with rational coefficients. That’s like, literally part of the definition. They cannot be compared to rational numbers like fractions.Since
|r|<1 => ∑[n=1, ∞] arⁿ = ar/(1-r), and0.999...is that sum witha = 9andr = 1/10(visually,0.999... = 9(0.1) + 9(0.01) + 9(0.001) + ...), it’s easy to see after plugging in,0.999... = 9(1/10) / (1 - 1/10) = 0.9/0.9 = 1). This was a proof present in Euler’s Elements of Algebra.pi isn’t even a fraction. like, it’s actually an important thing that it isn’t
pi=c/d
it’s a fraction, just not with integers, so it’s not rational, so it’s not a fraction.
The problem is, that’s exactly what the … is for. It is a little weird to our heads, granted, but it does allow the conversion. 0.33 is not the same thing as 0.333… The first is close to one third. The second one is one third. It’s how we express things as a decimal that don’t cleanly map to base ten. It may look funky, but it works.