نکته: جواب کلی معادلات مثلثاتی $Co{{t}^{2}}u=\operatorname{Co}{{t}^{2}}\alpha ,{{\tan }^{2}}u={{\tan }^{2}}\alpha ,{{\operatorname{Cos}}^{2}}u={{\operatorname{Cos}}^{2}}\alpha ,{{\operatorname{Sin}}^{2}}u={{\operatorname{Sin}}^{2}}\alpha $ عبارت است از: $u=k\pi \pm \alpha $  \[_{\operatorname{Sin}(\frac{\pi }{2}+x)=\operatorname{Cos}x,\operatorname{Cos}(-x)=\operatorname{Cos}x\Rightarrow \frac{1}{4}=\operatorname{Cos}x\times \operatorname{Cos}x\Rightarrow {{\operatorname{Cos}}^{2}}x=\frac{1}{4}={{\operatorname{Cos}}^{2}}\frac{\pi }{3}\Rightarrow x=k\pi \pm \frac{\pi }{3}}^{{{\operatorname{Sin}}^{2}}\frac{5\pi }{6}={{\operatorname{Sin}}^{2}}(\pi -\frac{\pi }{6})={{\operatorname{Sin}}^{2}}\frac{\pi }{6}={{(\frac{1}{2})}^{2}}=\frac{1}{4}}\]