Question 741244
Find all solutions in the interval [0, 2pi)
Cos^2 (x/2) = cos^2 x
{{{cos^2(x/2)=cos^2(x)}}}
{{{cos(x/2)=sqrt((1+cos(x))/2))}}}
{{{(1+cos(x))/2=cos^2(x)}}}
2cos^2(x)-cos(x)-1=0
(2cos(x)+1)(cos(x)-1)=0
cos(x)=-1/2
x=2&#960;/3, 4&#960;/3 (in Q2 and Q3 where cos<0)
cos(x)-1=0
cos(x)=1
x=0