Q. $\overrightarrow{A} = 3\widehat{i} - \widehat{j} + 7\widehat{k}$ and $\overrightarrow{B} = 5\widehat{i} - \widehat{j} + 9\widehat{k}$ the direction cosine $m$ of the vector $\overrightarrow{A} + \overrightarrow{B}$ is
A) Zero
B) $\frac{3}{\sqrt{31}}$
C) $\frac{9}{\sqrt{107}}$
D) 5
Explanation
(a) $\overrightarrow{A} + \overrightarrow{B}$=8$\widehat{i} - 2\widehat{j} + 16\widehat{k}$
$m = \frac{0}{\left| \overrightarrow{A} + \overrightarrow{B} \right|} = 0$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.