Question

What is the sum of the squares of direction cosines of $x$-axis?

• A. $0$
• B. $\frac{1}{3}$
• C. $1$
• D. $3$

Answer 1

Answer: (C)

$1$

The direction cosines of the vector a are the cosines of angles that the vector forms with the coordinate axes.

The direction cosines uniquely set the direction of vector.

$\therefore$ The sum of the squares of the direction cosines is equal to one.

$i.e.co{s}^2\alpha +co{s}^2\beta +co{s}^2\gamma =1$

Option C is correct answer