Differential Equations Question 38

Question: If $ \frac{dy}{dx}={e^{-2y}} $ and $ y=0 $ when $ x=5, $ the value of x for $ y=3 $ is

[MP PET 2001]

Options:

A) $ e^{5} $

B) $ e^{6}+1 $

C) $ \frac{e^{6}+9}{2} $

D) $ {\log _{e}}6 $

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Answer:

Correct Answer: C

Solution:

$ \int _{{}}^{{}}{\frac{dy}{{e^{-2y}}}}=\int _{{}}^{{}}{dx} $

Therefore $ \frac{e^{2y}}{2}=x+c $

At $ x=5,\ y=0 $

Therefore $ c=-\frac{9}{2} $ ;
$ \therefore $ $For $ y=3,\ x=\frac{e^{6}+9}{2} $ .