A Level

MATHEMATICS · Subjective · A Level · Mathematics · Trigonometry · Trigonometry

Problem

Prove that (cos⁡α+cos⁡β)2+(sin⁡α+sin⁡β)2=4cos⁡2(α−β2).(\cos \alpha + \cos \beta)^2 + (\sin \alpha + \sin \beta)^2 = 4 \cos^2 \left( \frac{\alpha - \beta}{2} \right).

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