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+--- Thread: What should be the correct range of acot function (/thread-15146.html)
What should be the correct range of acot function - teerasak - 06-06-2020 06:42 AM
As in the book, the range of acot(x) is 0 to pi
But when I check in HP prime by plotting acot(x) function, the range is -pi/2 to pi/2
Also, in wolfram alpha, the range is -pi/2 to pi/2
In TI-Nspire, the range is 0 to pi
What should be the correct one?
RE: What should be the correct range of acot function - anyfoo - 06-06-2020 06:52 AM
Matlab also uses -pi/2 to pi/2. Both are valid ranges, and so would be e.g. 2pi to 3pi, although unusual. The cotangent, like the other trigonometric function, repeats with multiples of pi, so to define a function that is suitable for use as its inverse, you can take any interval of pi.
RE: What should be the correct range of acot function - teerasak - 06-06-2020 08:50 AM
Thank you, anyfoo. I understand that the function is defined as interval of pi. But when referring to a standard function, it must have an agreed range e.g asin(x) - the range is -pi/2 to pi/2, acos(x) is 0 to pi. Just see that acot has different range in calculation tools and the book.
RE: What should be the correct range of acot function - pinkman - 06-06-2020 01:20 PM
(06-06-2020 08:50 AM)teerasak Wrote: Thank you, anyfoo. I understand that the function is defined as interval of pi. But when referring to a standard function, it must have an agreed range e.g asin(x) - the range is -pi/2 to pi/2, acos(x) is 0 to pi. Just see that acot has different range in calculation tools and the book.
In “my” books, tangent is defined from ]-π/2, π/2[ to ℝ
And it’s reciprocal cotangent is defined from ℝ to ]-π/2, π/2[, but US Wikipedia says ]0, π[
RE: What should be the correct range of acot function - ijabbott - 06-06-2020 02:34 PM
IMHO, since the "co" stands for "complementary", it seems to make more sense from a language point of view for atan(x) + acot(x) (in radians mode) to sum to pi/2 in the same way than asin(x) + acos(x) sum to pi/2.
RE: What should be the correct range of acot function - Wes Loewer - 06-06-2020 03:09 PM
There is no consensus on the range of the acot(x) function.
Using -pi/2 < y < pi/2 comes from defining acot(x)=atan(1/x), consistent with asec(x)=acos(1/x) and acsc(x)=asin(1/x)
Using 0 < y < pi comes from defining acot(x)=supplement of atan(x), consistent with acos(x)=supplement of asin(x) and acsc(x)=supplement of asec(x).
Most US textbooks use (0,pi), but a few use (-pi/2,pi/2), and many simply don't mention acot at all. Each has its advantage: (0,pi) is continuous but (-pi/2,pi/2) preserves odd symmetry and can be calculated more precisely for negative values of x.
I bring up this issue in my Precalc class each year and have the students argue for their preference. Makes for a fun discussion.
The nice thing about standards is that you have so many to choose from. ~Andrew Tanenbaum
----
Edit: Sorry, I meant "complement" above, not "supplement." That's where the "co" in cosine, cotangent, and cosecant comes from.
RE: What should be the correct range of acot function - teerasak - 06-06-2020 05:39 PM
Thank you for clarification. That clarifies my doubt.
RE: What should be the correct range of acot function - Wes Loewer - 06-07-2020 01:33 AM
Quote: Using 0 < y < pi comes from defining acot(x)=supplement of atan(x)
Woops. I meant complement, not supplement. That's what cosine means: the complement sine.
(We don't have to mention this little error to my students. :-) )
RE: What should be the correct range of acot function - Albert Chan - 03-21-2021 06:21 PM
(06-06-2020 03:09 PM)Wes Loewer Wrote: There is no consensus on the range of the acot(x) function.
All these programs have range of acot(x) = [-pi/2, pi/2]:
1. Mathematica
2. Sympy
3. Maxima
4. Python mpmath
5. XCas
6. HP Prime, both Home + Cas
Is there any exceptions you know ? (e.g. acot(-1) return 3/4*pi, instead of -1/4*pi ?)
RE: What should be the correct range of acot function - Felix Gross - 03-25-2021 06:58 AM
Excel (Version 16.46 for Mac)
ARCCOT(-1) =2,35619449
Documentation states that the results of ARCCOT are in the range between 0 and Pi
Felix
RE: What should be the correct range of acot function - Wes Loewer - 03-25-2021 07:14 PM
(03-21-2021 06:21 PM)Albert Chan Wrote: All these programs have range of acot(x) = [-pi/2, pi/2]:
1. Mathematica
2. Sympy
3. Maxima
4. Python mpmath
5. XCas
6. HP Prime, both Home + Cas
7. Google Sheets
(03-21-2021 06:21 PM)Albert Chan Wrote: Is there any exceptions you know ? (e.g. acot(-1) return 3/4*pi, instead of -1/4*pi ?)
. Excel, OpenOffice/LibreOffice, Quattro Pro
. Desmos
. GeoGebra (Well, sort of. It converts acot(x) to "pi/2-atan(x)")
. TI-Nspire
Not a program, but https://en.wikipedia.org/wiki/Inverse_trigonometric_functions#Principal_values.
RE: What should be the correct range of acot function - Felix Gross - 03-25-2021 10:49 PM
Here some more data points
-pi /2 to pi/2:
8. Sage: acot(-1) = -1/4 PI
9. Matlab (as already mentioned in the thread)
10. NIST Handbook of Mathematical Functions, 2010, p 112, Fig. 4.15.4
0 to pi:
Grapher (Mac program)
Edit: Added NIST reference