If A+B+C = 180 degree then prove that cosA + cos B - cosC = -1 + 4 cosA2 cosB2 sinC2 .

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

Matching exercise

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

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