Trigonometric inequality

Prove that the following inequality holds in any triangle:

    \[\left ( \sin \frac{A}{2} + \sin \frac{B}{2} \right )^2 + \left ( \sin \frac{B}{2} + \sin \frac{C}{2} \right )^2 + \left ( \sin \frac{C}{2} + \sin \frac{A}{2} \right )^2 \leq 3\]

Solution

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