A) \[\frac{\pi }{3}\]
B) \[\frac{\pi }{3},{{\cos }^{-1}}\frac{3}{5}\]
C) \[{{\cos }^{-1}}\frac{3}{5}\]
D) \[\frac{\pi }{3},\pi -{{\cos }^{-1}}\frac{3}{5}\]
Correct Answer: D
Solution :
\[5\cos 2\theta +2{{\cos }^{2}}\frac{\theta }{2}+1=0\] \[\Rightarrow \] \[5(2{{\cos }^{2}}\theta -1)+(1+\cos \theta )+1=0\] \[\Rightarrow \] \[10{{\cos }^{2}}\theta +\cos \theta -3=0\] \[\Rightarrow \] \[(5\cos \theta +3)\,(2\cos \theta -1)=0\] \[\Rightarrow \] \[\cos \theta =\frac{1}{2},\,\cos \theta =-\frac{3}{5}\Rightarrow \theta =\frac{\pi }{3},\,\pi -{{\cos }^{-1}}\left( \frac{3}{5} \right)\].
You need to login to perform this action.
You will be redirected in
3 sec
