tentukan nilai Sin 2 alfa ,Cos 2 alfa, dan tan 2 alfa, jika diketahui Cos Alfa 2/3

[tex] \cos( \alpha ) = \frac{2}{3} \\ \sin( \alpha ) = \sqrt{1 - {cos}^{2} \alpha } = \sqrt{1 - \frac{4}{9} } = \frac{ \sqrt{5} }{3} [/tex]
[tex] \sin(2 \alpha ) = 2( \frac{ \sqrt{5} }{3} )( \frac{2}{3} ) = \frac{4 \sqrt{5} }{9}[/tex]
[tex] \cos(2 \alpha ) = {( \frac{2}{3} )}^{2} - {( \frac{ \sqrt{5} }{3} )}^{2} = \frac{4}{9} - \frac{5}{9} = - \frac{1}{9} [/tex]
[tex] \tan(2 \alpha ) = \frac{ \sin(2 \alpha ) }{ \cos(2 \alpha ) } = - 4 \sqrt{5} [/tex]