A) \[[(1+m)/(1-m)]\tan \phi \]
B) \[[(1-m)/(1+m)]\tan \phi \]
C) \[[(1-m)/(1+m)]cot\phi \]
D) \[[(1+m)/(1-m)]sec\phi \]
Correct Answer: C
Solution :
We have \[\cos (\theta +\phi )=mcos(\theta -\phi )\] \[\Rightarrow \]\[\cos \theta \cos \phi -sin\theta \sin \phi \] \[=m(cos\theta \cos \phi \text{+}\,\text{sin}\theta \sin \phi )\] \[\Rightarrow \]\[\cos \theta \cos \phi (1-m)=\sin \theta \sin \phi (1+m)\] \[\Rightarrow \] \[\tan \theta =\left( \frac{1-m}{1+m} \right)\cot \phi \]
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