A) -1
B) 0
C) 1
D) 2
Correct Answer: C
Solution :
\[\cos 2\alpha +\cos 2\beta +\cos 2\gamma +\] \[{{\sin }^{2}}\alpha +{{\sin }^{2}}\alpha +{{\sin }^{2}}\beta +{{\sin }^{2}}\gamma \] \[=(co{{s}^{2}}\alpha -{{\sin }^{2}}\alpha )+(co{{s}^{2}}\beta -{{\sin }^{2}}\beta )\] \[({{\cos }^{2}}\gamma -{{\sin }^{2}}\gamma )+{{\sin }^{2}}\alpha +{{\sin }^{2}}\beta +{{\sin }^{2}}\gamma \] \[={{\cos }^{2}}\alpha +{{\cos }^{2}}\beta +{{\cos }^{2}}\gamma =1\]
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