tan(rad)
Calculates the ratio of the sine and cosine of an angle. This function expects the values of the angle parameter to be provided in radians (values from 0 to PI * 2). Values are returned in the range infinity to -infinity.
Type: function
Parameter(s):
- rad {Number}:A value in radians. 
Returns:
- 
    {Number}:
 The tangent value.