Expand Using Sum/Difference Formulas sin((3pi)/7)cos((2pi)/21)-cos((3pi)/7)sin((2pi)/21)

$\sin (\frac{3 π}{7}) \cos (\frac{2 π}{21}) - \cos (\frac{3 π}{7}) \sin (\frac{2 π}{21})$

Step 1

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$\sin (\frac{3 π}{7}) \cos (\frac{2 π}{21}) - \cos (\frac{3 π}{7}) \sin (\frac{2 π}{21})$