Question

The value of (cos 60° cos 30° − sin 60° sin 30°) is
(a) 0
(b) $\frac{\sqrt{3}}{2}$
(c) $\frac{1}{2}$
(d) 1

Answer 1

(a) 0

$$\begin{gathered} \cos {60}^{\mathrm{o}}\cos {30}^{\mathrm{o}}-\sin {60}^{\mathrm{o}}\sin {30}^{\mathrm{o}} \\ =\left(\frac{1}{2}\times \frac{\sqrt{3}}{2}-\frac{\sqrt{3}}{2}\times \frac{1}{2}\right) \\ =\frac{\sqrt{3}}{4}-\frac{\sqrt{3}}{4} \\ =0 \end{gathered}$$