Question

Find the direction cosines of line joining points

(1, –1, –3) and (–1, 2, 3)

• A. $\frac{2}{7},\frac{3}{7},\frac{6}{7}$
• B. $\frac{- 2}{7},\frac{- 3}{7},\frac{- 6}{7}$
• C. $\mp \frac{2}{7}, \pm \frac{3}{7}, \pm \frac{6}{7}$
• D. None of these

Answer 1

Answer: (B)

$\frac{- 2}{7},\frac{- 3}{7},\frac{- 6}{7}$

Answer 2

Direction ratios are –1 –1, 2 + 1, 3 + 3 ̃ –2,3,6

\ D.C's are

$\pm \frac{- 2}{\sqrt{2^{2} + 3^{2} + 6^{2}}}, \pm \frac{3}{\sqrt{2^{2} + 3^{2} + 6^{2}}}, \pm \frac{6}{\sqrt{2^{2} + 3^{2} + 6^{2}}}$

= $\mp \frac{2}{7}, \pm \frac{3}{7}, \pm \frac{6}{7}$