Question

$16cos frac{ pi }{9} cos frac{2 pi }{9} cos frac{ 4pi }{9}$

Answer 1

 
 $cosfrac{pi}{9}=cos20\ 16*cos20*cos40*cos80=frac{16*sin20*cos20*cos40*cos80}{sin20}\ frac{8*sin40*cos40*cos80}{sin20 } = frac{4*sin80*cos80}{sin20} = frac{2*sin160}{sin20} = 2*1=2$