Question

The projections of a directed lines segment on the coordinate axes are $12, 4, 3$ . The direction cosines of the line are

• A. $\frac{12}{13},\frac{4}{13},\frac{3}{13}$
• B. $\frac{12}{13},\frac{4}{13},-\frac{3}{13}$
• C. $-\frac{12}{13},\frac{4}{13},\frac{3}{13}$
• D. $\frac{12}{13},-\frac{4}{13},-\frac{3}{13}$

Answer 1

Answer: (A)

$\frac{12}{13},\frac{4}{13},\frac{3}{13}$

Answer 2

Now, $\sqrt{12^2 + 4^2 + 3^2} = \sqrt{144 + 16 + 9}$
$= \sqrt{169} = 13$
$\therefore$ Required direction cosines are
$< \frac{12}{13}, \frac{4}{13}, \frac{3}{13} >$