Question:

Find the particular solution of the differential equation \( (1 + e^{2x})dy + (1 + y^2)e^x dx = 0 \), given that \( y(1) = 0 \).

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Always check if simple variable separation is possible before attempting more complex methods.
Ensure substitution is correctly substituted back before applying initial conditions.
Updated On: Sep 10, 2026
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Solution and Explanation

Concept:
• Variable Separable Method: Grouping \( y \) terms with \( dy \) and \( x \) terms with \( dx \).
• Particular Solution involves finding the integration constant \( C \) using boundary conditions.

Step 1:
Separate the variables
\[ (1 + e^{2x})dy = -(1 + y^2)e^x dx \] \[ \frac{dy}{1 + y^2} = -\frac{e^x}{1 + (e^x)^2} dx \]

Step 2:
Integrate both sides
\[ \int \frac{dy}{1 + y^2} = -\int \frac{e^x}{1 + (e^x)^2} dx \] For the RHS, put \( e^x = t \), so \( e^x dx = dt \). \[ \tan^{-1} y = -\int \frac{dt}{1 + t^2} = -\tan^{-1} t + C \] \[ \tan^{-1} y = -\tan^{-1} e^x + C \implies \tan^{-1} y + \tan^{-1} e^x = C \]

Step 3:
Use boundary condition to find \( C \)
Given \( y(1) = 0 \), substitute \( x = 1, y = 0 \): \[ \tan^{-1} 0 + \tan^{-1} e^1 = C \] \[ 0 + \tan^{-1} e = C \implies C = \tan^{-1} e \]

Step 4:
Write the particular solution
\[ \tan^{-1} y + \tan^{-1} e^x = \tan^{-1} e \]
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