DTOR()
 Converts from a degree to radian measure
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 Syntax

     DTOR(<nAngle>) --> nArc

 Argument

     <Angle>  Designates a valid angle measurement in degrees.

 Returns

     DTOR() returns the radian of the specified value.

 Description

     In addition to expressing angle measurements in degrees, you may also
     need to express an angle in radians.  With DTOR(), you can convert
     degree measurements into radians.

 Example

     Show some calculations accurate to 15th place:

     ? STR(DTOR(360), 18, 15)     // Result: 6.283185307179588
     ? STR(DTOR(180), 18, 15)     // Result: 3.141592653589794
     ? STR(DTOR(180.5), 18, 15)   // Result: 3.150319299849766
     ? STR(DTOR(720), 18, 15)     // Result: 12.566370614359180
     ? STR(DTOR(-180), 18, 15)    // Result:-3.141592653589794