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MHT CET · Maths · Differential Equations

The solution of \(\mathrm{e}^{y-x} \frac{\mathrm{d} y}{\mathrm{~d} x}=\frac{y(\sin x+\cos x)}{(1+y \log y)}\) is

  1. A \(\frac{\mathrm{e}^y}{y}=\mathrm{e}^x \sin x+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.
  2. B \(\mathrm{e}^y \log y=\mathrm{e}^x \cos x+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.
  3. C \(\mathrm{e}^y \log y=\mathrm{e}^x \sin x+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.
  4. D \(\mathrm{e}^y y=\mathrm{e}^x \sin x+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.
Verified Solution

Answer & Solution

Correct Answer

(C) \(\mathrm{e}^y \log y=\mathrm{e}^x \sin x+\mathrm{c}\), where \(\mathrm{c}\) is a constant of integration.

Step-by-step Solution

Detailed explanation

\(\begin{array}{ll} & \mathrm{e}^{y-x} \frac{\mathrm{d} y}{\mathrm{~d} x}=\frac{y(\sin x+\cos x)}{(1+y \log y)} \\ \therefore \quad & \mathrm{e}^y \frac{(1+y \log y)}{y} \mathrm{~d} y=\mathrm{e}^x(\sin x+\cos x) \mathrm{d} x \\ \therefore \quad & \int \mathrm{e}^y\left(\log y+\frac{1}{y}\right) \mathrm{d} y=\int \mathrm{e}^x(\sin x+\cos x) \mathrm{d} x \\ & \Rightarrow \mathrm{e}^y \log y=\mathrm{e}^x \sin x+\mathrm{c} \\ & \ldots\left[\because \int \mathrm{e}^x\left(\mathrm{f}(x)+\mathrm{f}^{\prime}(x)\right) \mathrm{d} x=\mathrm{e}^x \mathrm{f}(x)+\mathrm{c}\right]\end{array}\)
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