Question

The angle between the lines whose direction cosines are $\left(\frac{\sqrt{3}}{4}, \frac{1}{4}, \frac{\sqrt{3}}{2}\right)$ and $\left(\frac{\sqrt{3}}{4}, \frac{1}{4}, \frac{-\sqrt{3}}{2}\right)$ is

• A. $\pi$
• B. $\frac{\pi}{2}$
• C. $\frac{\pi}{3}$
• D. $\frac{\pi}{4}$

Answer 1

Answer: (C)

$\frac{\pi}{3}$

Answer 2

$\cos \theta=\left|\frac{\sqrt{3}}{4} \times \frac{\sqrt{3}}{4}+\frac{1}{4} \times \frac{1}{4}-\frac{\sqrt{3}}{2} \times \frac{\sqrt{3}}{2}\right|=\left(\frac{-1}{2}\right), \theta$ $=\frac{\pi}{3}$