you can break up arg(z-2/z+2) into arg(z-2) - arg(z+2), so sketch two vectors that intercept to make a right angle, (their args subtract to give pi/2), and you know from circle geometry that an angle at the circumference of a circle when subtended by the diameter of the circle will be a right angle, therefore you know its a circle, with its centre half way between the origin of the two intersecting vectors...so 0,0. but its a semi circle because if the vectors went into the negative half of the y axis, the arg would be negative if we are talking about the primary argument. id sketch it for you but im on a laptop and i cant stand the touch pad in paint