Problem:
Let be a regular hexagon with center and side length . Point is placed in the interior of the hexagon such that . Compute all possible values of .
Solutions — 2
Solution 1
Solution:
Point is the intersection of circles with diameter and . Thus, there are two possible intersection points. Since , the first point, , is the intersection of and , from which we can see as our first answer. Let be the other intersection point.
Let be the midpoint of and be the midpoint of . Then and , so is an isosceles trapezoid. By law of cosine on , we have
Moreover, by Ptolemy's theorem,
Combining the previous two equations gives .
Solution 2
Solution:
Recall the first paragraph of the previous solution that is the first point. Thus, the second point is the Miquel point of cyclic quadrilateral .
By a well-known property of Miquel point, if , then and are inverses with respect to the circumcircle of . Thus, .
One can compute as follows: from triangle , we get that . Thus, by power of point,
implying .