$$\color{rgb(0,0,255)}\theta$$

$$\color{rgb(0,0,0)}y = x$$

$$\color{rgb(0,127,0)}-\theta$$

$$\color{rgb(255,0,0)}\frac{\pi }{2 }- \theta$$

$$\color{rgb(0,0,255)}\cos \, \theta$$

$$\color{rgb(0,0,255)}\cos \, \theta$$

$$\color{rgb(127,0,0)}\sin \, \theta$$

$$\color{rgb(127,0,0)}\sin \, \theta$$

$$\color{rgb(0,0,0)}\begin{array}{l} {\cos\left( {\frac{\pi }{2 } - \theta } \right)= \sin \, \theta } \\ {\sin\left( {\frac{\pi }{2 } - \theta } \right)= \cos \, \theta } \end{array}$$