To convert from degrees to radians, you would divide by 180 and multiply by pi.
To convert from radians to degrees, you would divide by pi and multiply by 180.
Such functions may be defined in the following way:
(defun dtr ( a ) (* pi (/ a 180.0)))
(defun rtd ( a ) (* 180.0 (/ a pi)))
Provided with a tangent of 0.26 recurring, you can obtain the corresponding angle in radians using:
(atan 300 1125) = 0.260602 radians
Alternatively:
(atan 0.266666667) = 0.260602 radians
Using the rtd function defined above, you can convert this to degrees:
(rtd (atan 300 1125)) = 14.9314 degrees