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D Y D X + 1 + Y 2 Y = 0

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Question

\[\frac{dy}{dx} + \frac{1 + y^2}{y} = 0\]
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Solution

We have, 
\[\frac{dy}{dx} + \frac{1 + y^2}{y} = 0\]
\[\Rightarrow \frac{dy}{dx} = - \frac{\left( 1 + y^2 \right)}{y}\]
\[ \Rightarrow \frac{dx}{dy} = - \frac{y}{1 + y^2}\]
\[ \Rightarrow dx = \left( - \frac{y}{1 + y^2} \right)dy\]
Integrating both sides, we get
\[\int dx = \int\left( - \frac{y}{1 + y^2} \right)dy\]
\[ \Rightarrow x = \int\left( - \frac{y}{1 + y^2} \right)dy\]
\[\text{ Putting }1 + y^2 = t, \text{ we get }\]
\[2y dy = dt\]
\[ \therefore x = - \frac{1}{2}\int\frac{1}{t}dt\]
\[ \Rightarrow x = - \frac{1}{2}\log\left| t \right| + C\]
\[ \Rightarrow x = - \frac{1}{2}\log\left| 1 + y^2 \right| + C\]
\[ \Rightarrow x + \frac{1}{2}\log\left| 1 + y^2 \right| = C\]
\[\text{ Hence, }x + \frac{1}{2}\log\left| 1 + y^2 \right| =\text{ C is the required solution }.\]

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Chapter 21: Differential Equations - Exercise 22.06 [Page 38]

APPEARS IN

R.D. Sharma Mathematics Volume 1 and 2 [English] Class 12
Chapter 21 Differential Equations
Exercise 22.06 | Q 1 | Page 38

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