The source of the conflict that oppose PI and TAU

An enlightening discussion about pi and tau.

The source of the conflict that oppose PI and TAU

by Apostoli » Sat Oct 25, 2014 6:31 pm


All the problem betwen PI and TAU is comming of a bad definition of the notion of radian.
An angle is define like the SURFACE betwen too crossings lines, and NOT like an arc of circle.
So, if that, 360 degrees is equivalent to PI (PI*r2 , with r=1) and not to 2*PI.
With this definition of radian, we have the perfect eiPI=1 instead of eiPI=-1.
When I was yonger I have never liked this -1 but I didn't understood why.

That is the reason. A bad definition of the Radian.
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Re: The source of the conflict that oppose PI and TAU

by 1=0 » Sun Mar 19, 2017 11:26 am

There's good reason to define the radian as arc length/radius rather than sector area/radius squared, even if you don't count the fact that arclength is 1 dimensional and thus the most fundamental measurement or the factor of 1/2 in sector area coming from triangles.

Many things in trigonometry only work with radians and not any other system of measurement. With radians, cosine is the derivative of sine.
The Taylor series for all the trig functions and Euler's formula only work in radians. These things wouldn't work with areans. So changing radians won't work. If could just use any unit we wanted, we would probably just use revolutions, but unfortunately, there are certain things that radians are needed instead of rotations. (Luckily, though, we have a convenient conversion factor between revolutions and radians called tau).

Also, even if we redefined radians, Euler's identity wouldn't change because complex exponents still have the same values; all that would happen is that Euler's formula would become much more messy. We know Euler's formula works in terms of radians because by substituting iθ for x in the Taylor series for e^x, you end up with the Taylor series for cosine plus i times the Taylor series for sine, but those Taylor series only work in terms of radians, so Euler's formula only works in radians. Therefore e^(iπ) and e^(iτ) still have the same values. However, if you do want to have the perfect e^(iπ)=1 instead of e^(iπ)=-1, using tau instead of pi is the only way to do it. Changing a unit of angle measure doesn't change the value of an algebraic expression.

So what is the real source of the conflict? The real problem is a bad definition of pi. Pi's definition of circumference divided by DIAMETER is inconsistent with the definition of radians, arc length divided by RADIUS. Tau's definition as circumference divided by RADIUS is consistent, however.

Also, when you said radians are not defined like the arc of a circle, I think you must have meant a sector, not an arc. Radians are defined as arc length divided by radius, so they are actually defined exactly like an arc. A one radian sector has the extremely elegant definition as a sector whose boundaries are all the same length, and these boundaries are two radii and an arc.
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