[Inscribed angle, based on the diameter]

Find the geometric locus of points $M$ from which a given segment $A B$ is seen at a right angle.
If the median of a triangle is equal to half the side to which it is drawn, then the triangle is a right triangle. The median of a right triangle drawn from the vertex of the right angle is equal to half the hypotenuse.

## Answer

The circle with diameter $AB$ without points $A$ and $B$.

## Problem