Question

The number of straight lines that are equally inclined to the three-dimensional coordinate axes is

• A. 2
• B. 4
• C. 6
• D. 8

Answer 1

Answer: (C)

6

Answer 2

a = b = g ̃ cos² a + cos² b + cos² g = 1

̃ l = m = n = ± $1/\sqrt{3}$

\ four lines having D.C's

$\left( \frac { 1 } { \sqrt { 3 } } , \frac { 1 } { \sqrt { 3 } } , \frac { 1 } { \sqrt { 3 } } \right) ; \left( - \frac { 1 } { \sqrt { 3 } } , \frac { 1 } { \sqrt { 3 } } , \frac { 1 } { \sqrt { 3 } } \right) ;$ $\left( \frac{1}{\sqrt{3}},\frac{- 1}{\sqrt{3}},\frac{1}{\sqrt{3}} \right);\left( \frac{1}{\sqrt{3}},\frac{1}{\sqrt{3}},\frac{- 1}{\sqrt{3}} \right)$