Question

Evaluate:$\cos {225}^{\circ }-\sin {225}^{\circ }$

Answer 1

$\cos {225}^{\circ }-\sin {225}^{\circ }$

$=\cos ({180}^{\circ }+{45}^{\circ })-\sin ({180}^{\circ }+{45}^{\circ })$

$=-\cos {45}^{\circ }+\sin {45}^{\circ }$

$=-\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{2}}$

$=0$