Let be the altitudes of an acute triangle with . Line meets at , and line through parallel to meets and at and , respectively. Let be any poin on side such that . Prove that .
Solution
1. Setup and Given Information:
- Let be the altitudes of an acute triangle with .
- Line meets at .
- A line through parallel to meets at and at .
- Let be any point on side such that .
2. Objective:
- Prove that .
3. Key Observations:
- Since are altitudes, are the feet of the perpendiculars from respectively.
- is the line segment joining the feet of the altitudes from and .
- The line through parallel to implies that and .
4. Properties of Parallel Lines:
- Since and , quadrilateral is a parallelogram.
- This implies that and .
5. Cyclic Quadrilateral:
- Given , it implies that points lie on a circle (cyclic quadrilateral).
6. **Midpoint of :**
- Let be the midpoint of .
- Since is the intersection of and , and is parallel to and , is the midpoint of .
7. Symmetry and Lengths:
- By symmetry and properties of the cyclic quadrilateral, the distances from to and are not equal.
- Since , the configuration of the triangle and the cyclic nature of implies that .
8. Conclusion:
- Therefore, .
The final answer is .