نکته $\operatorname{Cos}2\varepsilon ={{\operatorname{Cos}}^{2}}\alpha -{{\operatorname{Sin}}^{2}}\alpha =2{{\operatorname{Cos}}^{2}}\alpha -1=1-2{{\operatorname{Sin}}^{2}}\alpha $  نکته $\operatorname{Sin}x=\operatorname{Sin}a\Rightarrow \left\{ _{x=(2k+1)\pi -a}^{x=2k\pi +a} \right.$  با استفاده از نكات بالا داريم: $\operatorname{Sin}x-\operatorname{Cos}2x=2\Rightarrow \operatorname{Sin}x-(1-2{{\operatorname{Sin}}^{2}}x)=2\Rightarrow 2{{\operatorname{Sin}}^{2}}x+\operatorname{Sin}x-3=0\Rightarrow \left\{ _{\operatorname{Sin}x=-\frac{3}{2}}^{\operatorname{Sin}x=1\Rightarrow x=2k\pi +\frac{\pi }{2}} \right.$