[Kowit Pat.]

1.
$cos(\frac{41\pi}{12}) = cos(\frac{7\pi}{4}+\frac{5\pi}{3})$

$cos(\frac{7\pi}{4}+\frac{5\pi}{3}) = cos\frac{7\pi}{4}cos\frac{5\pi}{3}-sin\frac{7\pi}{4}sin\frac{5\pi}{3}$

$ cos\frac{7\pi}{4}cos\frac{5\pi}{3}-sin\frac{7\pi}{4}sin\frac{5\pi}{3} = cos\frac{\pi}{4}cos\frac{\pi}{3}-(-sin\frac{\pi}{4})(-sin\frac{\pi}{3})$

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