arg refers to the size of the angle of a complex number placed in polar coordinates. I believe that this is a mistype in this question.
arc cos is the size of the angle whose cos is .47.
If you want to find arc cos(θ) = .47, then use a calculator to find the invCos(.47); usually done by pressing (2nd) (cos) and entering .47. If you wish your answer to be in degrees, it is approximately 62 degrees.