Question 1138385
{{{cos(x)*sin(x) = sin^2(x)}}}
{{{cos(x)*sin(x) - sin^2(x)=0}}}
{{{cos(x)*sin(x) - sin(x)*sin(x)=0}}}
{{{(cos(x)-sin(x))*sin(x)=0}}}
One of those 2 factor must be zero for the product to be zero.
{{{cos(x)-sin(x)=0}}} if and only if {{{cos(x)=sin(x)}}}
When {{{0<=x<2pi}}} ,
{{{sin(x)=0}}} if and only if {{{x=0}}} or {{{x=pi}}} , and
{{{cos(x)=sin(x)}}} if and only if {{{x=pi/4}}} or {{{x=5pi/4}}}