Expand Using Sum/Difference Formulas cos((13pi)/15)cos(-pi/5)-sin((13pi)/15)sin(-pi/5)

$\cos (\frac{13 π}{15}) \cos (- \frac{π}{5}) - \sin (\frac{13 π}{15}) \sin (- \frac{π}{5})$

Step 1

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$\cos (\frac{13 π}{15}) \cos (- \frac{π}{5}) - \sin (\frac{13 π}{15}) \sin (- \frac{π}{5})$