Find right triangle inscribed in circle from two points on separate legs

circleseuclidean-geometrygeometrytriangles

I am getting started on problem solving, and need help with the following exercise of "Solving mathematical problems, a personal perspective". The full question is as follows:

"We are given a circle and two points A and B inside the circle. If possible, construct a right-angled triangle inscribed in the circle such that one leg of the right-angled triangle contains A and the other leg contains B; see figure below. (Hint: solve for the right-angled vertex.)"

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I'm not familiar with these kinds of problems, and quite frankly don't know where to start. If you can provide an answer, could you please start it off with a hint, as I don't really want to be spoon-fed all the way. Thanks!

Best Answer

If $C$ is the right angle vertex of a triangle that satisfies the problem statement, note that $\triangle ABC$ is also a right triangle with right angle at $C.$

Find the set of all points that can be the right-angled vertex of a right triangle whose other vertices are $A$ and $B.$ The point $C$ cannot be anywhere except in that set of points.

Of course, $C$ must also be on the given circle.

You now have two facts about $C$ which can help you to find that point. (Note that there might be more than one choice or there might be none, depending on how the construction goes.)