Question

Find the value of
$\cos {60}^o\times \cos {30}^o+\sin {60}^o\times \sin {30}^o$

Answer 1

$\cos {60}^o\times \cos {30}^o+\sin {60}^o\times \sin {30}^o$
$=\frac{1}{2}\times \frac{\sqrt{3}}{2}+\frac{\sqrt{3}}{2}\times \frac{1}{2}$
$=\frac{\sqrt{3}}{4}+\frac{\sqrt{3}}{4}$
$=\frac{2\sqrt{3}}{4}$
$=\frac{\sqrt{3}}{2}$