Differential Equations Question 31

Question: The general solution of the differential equation $ \frac{dy}{dx}=\cot x\cot y $ is

[AISSE 1983; MP PET 1994]

Options:

A) $ \cos x=c\cos ecy $

B) $ \sin x=c\sec y $

C) $ \sin x=c\cos y $

D) $ \cos x=c\sin y $

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Answer:

Correct Answer: B

Solution:

$ \frac{dy}{dx}=\cot x\cot y $

Therefore $ \int _{{}}^{{}}{\tan ydy=\int _{{}}^{{}}{\cot xdx}} $

Therefore $ \log \sec y=\log \sin x+\log c $

Therefore $ \sec y=c\sin x $ or $ c\sec y=\sin x $ .