Question 1075523
2 cos^2 x-1=cos 2x
2 cos^2x-1+cos x=0
rewrite as 2 cos^2 x+cos x-1=0
(2 cos x-1)(cos x+1)=0
cos x=1/2
cos x=-1
This works at pi, pi/3 and 5pi/3
{{{graph(300,300,-6,6,-2,2,cos(2x)+cos(x))}}}