Question

cos 2x - cos x = 0. Find all solutions in interval [0,2pi]. I literally have no idea how to do this so a link to a youtube video or an explanation would be awesome

Answer 1

\[\cos2x=2\cos ^{2}x-1\]
\[(2cosx+1)(cosx-1)=0\]
\[\cos x=-0.5,1\]
between 0 and 2pi, therefore the solutions are
x=0, 2pi, 2pi/3, 4pi/3