Understand the problem
Determine when equality holds.
Source of the problem
Start with hints
Show that there exists a triangle such that and . The easiest way to prove is is to define , and show that must be .
Now the inequality becomes equivalent to . Take a look at this well-known inequality. Note that the tangent is a convex function in .
Using Jensen’s inequality, we get . Equality holds for an equilateral triangle.
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