Question 639141
{{{cos^2(x)=cos (x)}}}
{{{cos^2(x)-cos (x)=0}}}
{{{cos(x)(cos (x)-1)=0}}}
Use a property of zero
{{{cos(x)=0}}} or {{{cos(x)-1=0}}}
{{{x=pi/2}}}, {{{x=3pi/2}}} or {{{cos(x)=1}}}
{{{x=pi/2}}}, {{{x=3pi/2}}}  or {{{x=0}}}