Question

The value of $\cos 15^{\circ }\cos 7{\frac{1}{2}}^{\circ }\sin 7{\frac{1}{2}}^{\circ }$ is

• A. $\frac{1}{8}$
• B. $\frac{1}{16}$
• C. $\frac{1}{2}$
• D. $\frac{1}{4}$

Answer 1

Answer: (A)

$\cos 15^{\circ }\cos 7{\frac{1}{2}}^{\circ }=\frac{\left(2\sin 7{\frac{1}{2}}^{\circ }\cos 7{\frac{1}{2}}^{\circ }\right)\cos 15^{\circ }}{2}$
$=\frac{1}{2}\times \frac{1}{4}=\frac{1}{8}$