Let be a triangle and its incenter. Suppose , , and the inradius is . Let be the reflection of across , the reflection across , and the reflection across . Compute the area of triangle .
Solution
1. Identify the points of tangency and reflections:
Let be the points of tangency of the incircle with sides and respectively. The points are the reflections of the incenter across the sides and respectively.
2. Similarity of triangles:
Note that triangle is similar to triangle with a ratio of . This is because the reflections of the incenter across the sides of the triangle form a triangle that is homothetic to the contact triangle with a homothety ratio of .
3. **Area of triangle :**
To find the area of triangle , we first need to compute the area of the smaller triangles and .
4. **Area of triangle :**
By the Pythagorean theorem, we have:
Let be the intersection of and . Since triangle is similar to triangle , we have:
Similarly,
Therefore, the area of triangle is:
5. **Area of triangles and :**
By similar calculations, we find the areas of triangles and :
6. **Total area of triangle :**
Summing the areas of the three smaller triangles, we get:
7. **Area of triangle :**
Since triangle is similar to triangle with a ratio of , the area of is:
The final answer is