In the PROMOTIC system it is better to use the Pm.Atan method.
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To convert degrees to radians, multiply degrees by pi/180. To convert radians to degrees, multiply radians by 180/pi.
Atn is the inverse trigonometric function of Tan, which takes an angle as its argument and returns the ratio of two sides of a right triangle. Do not confuse Atn with the cotangent, which is the simple inverse of a tangent (cotangent=1/tangent).
pi = 4 * Atn(1) 'calculate the value of Pi
Dim Arcsin, Arccos, Arcsec, Arccosec, Arccotan
Arcsin = Atn(x / Sqr(-x * x + 1))
Arccos = Atn(-x / Sqr(-x * x + 1)) + 2 * Atn(1)
Arcsec = Atn(x / Sqr(x * x - 1)) + Sgn(x - 1) * 2 * Atn(1)
Arccosec = Atn(x / Sqr(x * x - 1)) + (Sgn(x) - 1) * 2 * Atn(1)
Arccotan = Atn(x) + 2 + Atn(1)