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MathNet 2010 — Part 06 Question 144

Math Olympiad Vault · MathNet 2010 — Part 06

Question 144

Let $h$ be the altitude of triangle $ABC$ passing through the vertex $A$ and $\alpha = \angle BAC$. Prove that the following inequality holds:
$$
AB + AC \ge BC \cdot \cos \alpha + 2h \sin \alpha.
$$
In what triangles does equality hold?