Question

Find the value of $\cos \,\,(29\pi /3)?$

• A. $1$
• B. $0$
• C. $\frac{\sqrt{3}}{2}$
• D. $1/2$

Answer 1

Answer: (D)

$1/2$

Answer 2

$\cos \left( 29\frac{\pi }{3} \right)=\cos \left( \frac{(27+2)\pi }{3} \right)$
$=\cos \left( 9\pi +\frac{2\pi }{3} \right)$
$=-\cos \frac{2\pi }{3}=-\cos \left( \frac{\pi }{2}+\frac{\pi }{6} \right)=\sin \frac{\pi }{6}=\frac{1}{2}$