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Question: Answered & Verified by Expert
The solution of $(2 \cos x-1)(3+2 \cos x)=0$ in the interval $0 \leq x \leq 2 \pi$ is
MathematicsTrigonometric EquationsBITSATBITSAT 2014
Options:
  • A $\frac{\pi}{3}$
  • B $\frac{\pi}{3}, \frac{5 \pi}{3}$
  • C $\frac{\pi}{3}, \frac{5 \pi}{3}, \cos ^{-1}\left(-\frac{3}{2}\right)$
  • D None of these
Solution:
2139 Upvotes Verified Answer
The correct answer is: $\frac{\pi}{3}, \frac{5 \pi}{3}$
We have $(2 \cos x-1)(3+2 \cos x)=0$

If $2 \cos x-1=0,$ then $\cos x=\frac{1}{2}$

$\therefore x=\pi / 3,5 \pi / 3$

If $3+2 \cos x=0,$ the $\cos x=-3 / 2$

which is not possible.

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