Question 429870
{{{cos(x+ pi/2) = cos(2x)}}}
In the interval [0, {{{2pi}}}), either 

{{{x+ pi/2 = 2x}}}, or {{{x + pi/2 = 2*pi - 2x}}}

==> {{{x = pi/2}}}, or 

{{{3x = (3*pi)/2}}}, or {{{x = pi/2}}} (Same as the first solution.)

Therefore the general solution is {{{pi/2 + 2n*pi}}}, where n is any integer.