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Trigonometry
Question

Find the exact value of \( \cos ( \alpha + \beta )...

Find the exact value of \( \cos ( \alpha + \beta ) \) if \( \sin \alpha = \frac { - 3 } { 5 } \) and \( \sin \beta = \frac { - 5 } { 13 } , \) with \( \alpha \) in quadrant III and \( \beta \) in quadrant III. 

\( \cos ( \alpha + \beta ) = \square \) 

(Simplify your answer. Type a fraction.) 

Answer

\(cos(\alpha + \beta )= cos\alpha cos\beta - sin\alpha sin\beta = \frac{33}{65}\)

Solution
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