Question 984641
{{{cos A=sqrt((1+cos(2A))/2)}}}
 put A=30
  then 
{{{Cos(30)=sqrt((1+cos(60))/2)}}}
{{{ cos(30)=sqrt((1+(1/2))/2)}}}
 {{{cos(30)= sqrt((3/2)/2)}}}
  {{{cos(30)= sqrt(3/4)}}}
   {{{cos(30)=sqrt(3)/2}}}