​ What is the value of arccos(−1) in radians?

Guest troll visits some strange websites.

Do you know where   cos(x) = -1  ?    This is true at   pi radians (or 180 degrees ----same thing)

    so    cos (pi) = -1

    now arcos both sides

        arcos ( cos(pi) )  = arcos (-1)

                     pi = arcos (-1)