Robin said:
It worked well, I do onot understand what is behind the excel
terminology concerning this.
Excel is using the math terms correctly. You are not; or perhaps the
markings on your calculator are misleading you.
And that begs the question: what is it that you really want to calculate:
the cotangent, as you indicated originally; or the arctangent, which is
shift+TAN on your calculator?
Whereas x^-1 (where "^" indicates superscript) is 1/x, tan^-1(x) is not
1/tan(x). 1/tan(x) might be written as tan(x)^-1.
The cotangent (cot) is 1/tan(x), the reciprocal of tan(x). The arctangent
(atan) is tan^-1(x), the inverse function of tan(x).
If f(x) = y, the inverse function g(y) = x. So, atan(tan(x)) = x.
On my HP-11C, blueshift+TAN is marked tan^-1, and it computes the
arctangent, not the cotangent 1/tan.
But that does not mean that's the right caculation for you to use. GIGO.
----- original message -----