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MHT CET · Maths · Differential Equations

The solution of the differential equation \(\log \left(\frac{\mathrm{dy}}{\mathrm{d} x}\right)=9 x-6 \mathrm{y}+6\) is
(given that \(\mathrm{y}=1\) when \(x=0\) )

  1. A \(3 e^{6 y}=2 e^{9 x-6}+e^{6}\)
  2. B \(3 e^{6 y}=2 e^{9 x+6}+e^{6}\)
  3. C \(3 e^{6 y}=2 e^{9 x+6}-e^{6}\)
  4. D \(3 e^{6 y}=2 e^{9 x-6}-e^{6}\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(3 e^{6 y}=2 e^{9 x+6}+e^{6}\)

Step-by-step Solution

Detailed explanation

\(\log \left(\frac{d y}{d x}\right)=9 x-6 y+6 \Rightarrow \frac{d y}{d x}=e^{9 x-6 y+6}\)
\(\therefore \frac{d y}{d x}=e^{9 x+6} \cdot e^{-6 y} \Rightarrow \frac{d y}{e^{-6 y}}=e^{9 x} \cdot e^{6} d x\)
\(\therefore \int e^{6 y} d y=e^{6} \int e^{9 x} d x\)
\(\frac{e^{6 y}}{6}=\frac{e^{6} e^{9 x}}{9}+C\)
We have \(x=0, y=1\)
\(\therefore \frac{e^{6}}{6}=\frac{e^{6}}{9}+C \Rightarrow C=\frac{e^{6}}{18}\)
\(\therefore \frac{e^{6 y}}{6}=\frac{e^{6} e^{9 x}}{9}+\frac{e^{6}}{18} \Rightarrow 3 e^{6 y}=2 e^{6+9 x}+e^{6}\)