Question

If a straight line in space is equally inclined to the co-ordinate axes, the cosine of its angle of inclination to any one of the axes is.

• A. $\frac { 1 } { 3 }$
• B. $\frac { 1 } { 2 }$
• C. $\frac { 1 } { \sqrt { 3 } }$
• D. $\frac { 1 } { \sqrt { 2 } }$

Answer 1

Answer: (C)

$\frac { 1 } { \sqrt { 3 } }$

Answer 2

Here, $\cos \alpha = \cos \beta = \cos \gamma$

$\therefore$ $3 \cos ^ { 2 } \alpha = 1 \Rightarrow \alpha = \cos ^ { - 1 } \left( \pm \frac { 1 } { \sqrt { 3 } } \right)$ .