Question 1034055
If you are asking to solve this...
{{{sin(theta) + cos(theta) = cos 2(theta)}}}
{{{sin(theta) + cos(theta) = (cos(theta))^2 - (sin(theta))^2}}}
{{{sin(theta) + cos(theta) = (cos(theta)+sin(theta))(cos(theta)-sin(theta))}}}
{{{1 = cos(theta)-sin(theta)}}}
{{{theta = 0}}} or {{{theta = 270}}}
Two more solutions exist...
{{{theta = 135}}} or {{{theta = 315}}}