[tex]221 \pi = 216 \pi + 5 \pi
=\ \textgreater \ \frac{221 \pi }{6} = \frac{216 \pi +5 \pi }{6} = \frac{216 \pi }{6} + \frac{5 \pi }{6} = 36 \pi + \frac{5 \pi }{6}
[/tex][tex]cos \frac{221 \pi }{6} = cos(36 \pi + \frac{5 \pi }{6} )=cos \frac{5 \pi }{6} =cos( \pi - \frac{ \pi }{6} ) = -cos \frac{ \pi }{6} =- \frac{ \sqrt{3} }{2} [/tex]
Sin si cos au perioada 2[tex] \pi [/tex]
