cos x + 2 cos^2(x/3) -3=0 <=> 4cos^3(x/3) - 3cos(x/3) + 2 cos^2(x/3) -3 =0 <=> cos(x/3) =1 <=> x = 6k$\Pi$ ( k $\in$ Z)
cos x + 2 cos^2(x/3) -3=0 <=> 4cos^3(x/3) - 3cos(x/3) + 2 cos^2(x/3) -3 =0 <=> cos(x/3) =1 <=> x = 6k\Pi ( k \in Z)
cos x + 2 cos^2(x/3) -3=0 <=> 4cos^3(x/3) - 3cos(x/3) + 2 cos^2(x/3) -3 =0 <=> cos(x/3) =1 <=> x = 6k
$\Pi
$ ( k
$\in
$ Z)