Thank mr fantastic,
Here is my partial solution.
Separation of the variables:
Right side of the equation:
Did I wrote the equation correctly? Correct me if I am wrong.
Left side of the equation:
I'm stucked in this point. How can I go to the answer (left side of the equation)?
I think this theorem would be help. But I am not sure how to go to the answer.
Theorem: Inverse Trigonometric Functions
Thanks to all.