Question

The angle between two vectors $- 2\widehat{i} + 3\widehat{j} + \widehat{k}$ and $\widehat{i} + 2\widehat{j} - 4\widehat{k}$ is

• A. 0°
• B. 90°
• C. 180°
• D. None of the above

Answer 1

Answer: (B)

90°

Answer 2

$\cos\theta = \frac{\overrightarrow{A}.\overrightarrow{B}}{|\overrightarrow{A}||\overrightarrow{B}|} = \frac{- 2 + 6 - 4}{\sqrt{14}\sqrt{21}} = 0$ ∴ $\theta = 90{^\circ}$