Mathematics

Mathematics

Problem

Which of the following expressions is equal to cos⁡(x−y)\cos(x-y) for any angles xx and yy? a) cos⁡xcos⁡y−sin⁡xsin⁡y\cos x\cos y-\sin x\sin y b) sin⁡xcos⁡y−cos⁡xsin⁡y\sin x\cos y-\cos x\sin y c) cos⁡xcos⁡y+sin⁡xsin⁡y\cos x\cos y+\sin x\sin y d) cos⁡xcos⁡y\cos x\cos y

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