A and B are two fixed points. A point P moves in the plane so that angle APB is always a right angle. Which statement about the path of P is TRUE?

The angle in a semicircle is a right angle, so every point of the circle on AB as diameter (other than A and B) sees AB at 90°. Conversely, if angle APB = 90° then P is at distance AB/2 from the midpoint of AB, because the median to the hypotenuse of a right triangle is half the hypotenuse — so P lies on that circle. A and B are excluded since no angle is formed there. Note the radius is AB/2, not AB.