Inverse trigonometric functions



Hello,

Does anyone know if it's possible with Maxima to compute expressions
such as Machin's formula:
pi/4=4arctan(1/5)-arctan(1/239)

or formula such as:

cos(1/2*arccos(1/3))=sqrt(6)/3

If it's impossible, does anyone know if someone plan to implement it in
Maxima?

Best

Lo?c