kill(all)$

     Van / 2015 / facebook.com/LearningCalculus

Radians(degrees) := (%pi/180)*degrees$
Degrees(radians) := (180/%pi)*radians$
Radians(180); Degrees(%pi);

load(ntrig)$

atan(a/2 - 1/(2*a));

Degrees(%);

float(substitute(3,a,%));