This is the concept of algebra, to solve the expression we proceed as follows; cos 2x-cosx=0 cos 2x=cosx but: cos 2x+1=2(cos^2x) thereore; from: cos 2x=cos x adding 1 on both sides we get: cos 2x+1=cos x+1 2(cos^2x)=cosx+1 suppose; cos x=a thus; 2a^2=a+1 a^2-1/2a-1/2=0 solving the above quadratic we get: a=-0.5 and a=1 when a=-0.5 cosx=-0.5 x=120=2/3π when x=1 cos x=1 x=0 the answer is: x=0 or x=2/3π
