[Python-ideas] Trigonometry in degrees

Steven D'Aprano steve at pearwood.info
Fri Jun 8 02:22:07 EDT 2018

On Fri, Jun 08, 2018 at 02:37:33PM +0900, Stephen J. Turnbull wrote:

> My bias is that people who want to program this kind of thing just
> need to learn about floating point numbers and be aware that they're
> going to have to accept that
> >>> from math import cos, radians
> >>> cos(radians(90))
> 6.123233995736766e-17
> >>> 
> is good enough for government work, including at the local public high
> school.

In Australia, most secondary schools recommend or require CAS 
calculators from about Year 10, sometimes even from Year 9. Most (all?) 
state curricula for Year 11 and 12 mandate CAS calculators. Even 
old-school scientific calcuators without the fancy CAS symbolic maths 
are capable of having cos(90) return zero in degree mode.

It is quite common for high school students to expect cos(90°) to come 
out as exactly zero. And why not? It's the 21st century, not 1972 when 
four-function calculators were considered advanced technology :-)

To my mind, the question is not "should we have trig functions that take 
angles in degrees" -- that's a no-brainer, of course we should. The only 
questions in my mind are whether or not such a library is (1) 
appropriate for the stdlib and (2) ready for the stdlib.


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