If A+B+C = 180 degree then prove that cosA + cos B + cosC = 1 + 4 sinA2sinB2 sinC2 .

If A+B+C = 180 degree then prove that $\cos A + \cos B + \cos C = 1 + 4 \sin \frac{A}{2} \sin \frac{B}{2} \sin \frac{C}{2}$ .

Matching exercise

Match the items on the right to the items on the left.

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