These are the tangent and arctangent functions, from which all the other trigonometric functions are defined.
The standard trigonometric functions and their inverses.
(%0051) tan(atan(x));
%0051: x
(%0052) atan(tan(x));
%0052: x
(%0053) tan(2*atan(x));
2 x
%0053: ------
2
1 - x
(%0054) tan(3*atan(x));
3
- 3 x + x
%0054: ----------
2
-1 + 3 x
(%0055) tan(4*atan(x));
3
- 4 x + 4 x
%0055: --------------
2 4
-1 + 6 x - x
(%0056) atan(2*tan(x));
%0056: atan(2 tan(x))
(%0057) sin(3*asin(x));
3
%0057: - 3 x + 4 x