If the direction cosines of a line are 1/c,1/c, 1/c, then

If $\frac{1}{c},\frac{1}{c}, \frac{1}{c}$ are the direction cosines of a line, then $\frac{1}{c^2}+\frac{1}{c^2}+\frac{1}{c}=1 ⇒ c =± \sqrt{3} $