Some helpers functions are currently useless and leads to computations of arccos (with many rounding errors).

The aim of the patch is to remove that and simplify the code a bit.

WIP:

- I would perhaps write a test or something like that
- Need to check the types things
- We could compute only one cos - sin and then only use multiplications but with compounded approx we have sometimes weird results, so I prefer skip that for the moment