A) A is true and B is false
B) A is false and B is true
C) both A and B are true
D) both A and B are false
Correct Answer: C
Solution :
\[cos(\beta \gamma )+cos(\gamma \alpha )+cos(\alpha \beta )=3/2\] \[\Rightarrow \]\[2cos(\beta \gamma )+2cos(\gamma \alpha )+2cos(\alpha \beta )=3\] \[\Rightarrow \] \[\Sigma (cos\beta cos\gamma +2\Sigma sin\text{ }sin\beta +3=0\] \[\Rightarrow \] \[{{(\cos \alpha +\cos \beta +\cos \gamma )}^{2}}+\] \[{{(\sin \alpha +\sin \beta +\sin \gamma )}^{2}}=0\] \[\Rightarrow \] \[cos\alpha +cos\beta +cos\gamma =0\] \[sin\alpha +sin\alpha +sin\gamma =0\]
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