What should be the correct range of acot function

[teerasak]

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.