VB中反余弦的问题？？？？？

网上有些是Arccos(X) = Atn(-X / Sqr(-X * X + 1)) + 2 * Atn(1) 有些又是Function ArcCos(x As Double) As Double
   If x >= -1 And x < -0.5 Then ArcCos = Atn(Sqr(1 - x * x) / x) + 4 * Atn(1)
   If x >= -0.5 And x <= 0.5 Then ArcCos = -Atn(x / Sqr(1 - x * x)) + 2 * Atn(1)
   If x > 0.5 And x <= 1 Then ArcCos = Atn(Sqr(1 - x * x) / x)
   ArcCos = ArcCos / 3.1415926 * 180
End Function请问哪一个能计算任意幅度值的公式？？？