A) \[45{}^\circ \]
B) \[60{}^\circ \]
C) \[30{}^\circ \]
D) \[90{}^\circ \]
Correct Answer: D
Solution :
Given,\[l=cos\text{ }45{}^\circ ,\text{ m}=cos\text{ }45{}^\circ and\,z=cos\text{ }\theta \] \[\because \] \[{{l}^{2}}+{{m}^{2}}+{{n}^{2}}=1\] \[\Rightarrow \] \[co{{s}^{2}}45{}^\circ +co{{s}^{2}}45{}^\circ +co{{s}^{2}}\theta =1\] \[\Rightarrow \] \[\frac{1}{2}+\frac{1}{2}+{{\cos }^{2}}\theta =1\] \[\Rightarrow \] \[{{\cos }^{2}}\theta =0\] \[\Rightarrow \] \[\theta =90{}^\circ \]
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