Impartim ecuatia la cos^2 x, notam tg x =t si avem:
[tex]-3t^2-2t+1=0[/tex] cu solutiile:
[tex]t_1=-1;\ t_2=\dfrac13[/tex]
[tex]tg x=-1\Rightarrow x_k=-\dfrac{\pi}{4}+k\pi;\ k\in Z[/tex]
[tex]tgx= \dfrac13\Rightarrow x_k=arctg\dfrac13+k\pi; k\in Z[/tex]