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JEE Main 2018
Trigonometric Equations
Trigonometric Equations
Easy

Question

The number of solutions of the equation cotx=cotx+1sinx|\cot x| = \cot x + {1 \over {\sin x}} in the interval [ 0, 2π\pi ] is

Answer: 0

Solution

Case I : When cot x > 0, x[0,π2][π,3π2]x \in \left[ {0,{\pi \over 2}} \right] \cup \left[ {\pi ,{{3\pi } \over 2}} \right] cotx=cotx+1sinx\cot x = \cot x + {1 \over {\sin x}} \Rightarrow not possible Case II : When cot x < 0, x[π2,π][3π2,2π]x \in \left[ {{\pi \over 2},\pi } \right] \cup \left[ {{{3\pi } \over 2},2\pi } \right] cotx=cotx+1sinx - \cot x = \cot x + {1 \over {\sin x}} 2cosxsinx=1sinx \Rightarrow {{ - 2\cos x} \over {\sin x}} = {1 \over {\sin x}} cosx=12 \Rightarrow \cos x = {{ - 1} \over 2} x=2π3,4π3 \Rightarrow x = {{2\pi } \over 3},{{4\pi } \over 3}(Rejected) One solution.

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