If , ,then evaluate .

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

Problem

If cos⁡α=12(x+1x)\cos \alpha = \frac{1}{2} \left( x + \frac{1}{x} \right) , cos⁡β=12(y+1y)\cos \beta = \frac{1}{2} \left( y + \frac{1}{y} \right) ,then evaluate cos⁡(α−β)\cos(\alpha - \beta) .

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