Объяснение:

[tex]cos(\frac{\pi }{3}+\alpha )+cos(\frac{\pi }{3} -\alpha )=cos\frac{\pi }{3}*cos\alpha -sin\frac{\pi }{3}*sin\alpha +cos\frac{\pi }{3}*cos\alpha +sin\frac{\pi }{3}*sin\alpha =\\[/tex]

[tex]=2*cos\frac{\pi }{3}*cos\alpha =2*\frac{1}{2}*cos\alpha =cos\alpha =\frac{1}{9}.[/tex]