ATANR()
 To return the ARCTANGENT in radians of a tangent value.
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 Syntax

      ATANR( <nTan> ) -> nRadian

 Arguments

      <nTan> is a numeric value representing a tangent value.

      NOTE: Since a parameter of greater than 1 result in a math overflow,
            this function returns 0 as a result instead of a math overflow.

 Returns

      ATANR() returns the arctangent value (reverse tangent) in radians of
      <nTan>.

 Description

      ATANR() is a trigonometrical function that returns the arctangent value
      in radians of a tangent value.

      For degrees, see ATAN().

      Accuracy is to the twelfth decimal (i.e. .00000000001)

 Examples

      ? Str( ATANR(.707106781), 8,  6)  // returns 0.615480
      ? Str( ATANR(.866025403), 8,  6)  // returns 0.713724

 Files: CALC.LIB

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