\frac{1}{3}\\\\-arccos\frac{1}{3}+2\pi n\, <3t<\, arccos\frac{1}{3}+2\pi n\; ,\; \; n\in Z\\\\-\frac{1}{3}arccos\frac{1}{2}+\frac{2\pi n}{3}\, <t<\, \frac{1}{3}arccos\frac{1}{3}+\frac{2\pi n}{3}\; ,\; \; n\in Z" alt="cos\, 3t>\frac{1}{3}\\\\-arccos\frac{1}{3}+2\pi n\, <3t<\, arccos\frac{1}{3}+2\pi n\; ,\; \; n\in Z\\\\-\frac{1}{3}arccos\frac{1}{2}+\frac{2\pi n}{3}\, <t<\, \frac{1}{3}arccos\frac{1}{3}+\frac{2\pi n}{3}\; ,\; \; n\in Z" align="absmiddle" class="latex-formula">
