kill(all)$ load(atrig1)$ load(ntrig)$ solveprint:false$

Van=facebook.com/LearningCalculus;

f(x):=2*sin(x)^2-cos(x)-1=0;

g(x):=ratsimp(subst(1-cos(x)^2,sin(x)^2,f(x)));

solve(g(x),x)$

Symmetry$

[pi-2*pi/3,pi,pi+2*pi/3];