Question

Find the value of $\cos {210}^{\circ }\sin {300}^{\circ }$

Answer 1

$\cos {210}^{\circ }\sin {300}^{\circ }$

$=\cos ({180}^{\circ }+{30}^{\circ })\sin ({360}^{\circ }-{60}^{\circ })$

$=-\cos {30}^{\circ }\times -\sin {60}^{\circ }$

$=-\frac{\sqrt{3}}{2}\times \frac{-\sqrt{3}}{2}$

$=\frac{3}{4}$