A) \[\frac{2\pi }{3}\]
B) \[\frac{\pi }{6}\]
C) \[\frac{5\pi }{6}\]
D) \[\frac{\pi }{3}\]
Correct Answer: D
Solution :
\[l+m+n=0,\,\,{{l}^{2}}+{{m}^{2}}-{{n}^{2}}=0\] and \[{{l}^{2}}+{{m}^{2}}+{{n}^{2}}=1\] Solving above equations, we get \[m=\pm \frac{1}{\sqrt{2}},\,\,n=\pm \frac{1}{\sqrt{2}}\] and \[l=0\]. \[\therefore \,\,\,\theta =\frac{\pi }{3}\] or \[\frac{\pi }{2}\].
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