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MHT CET · Maths · Differential Equations

The general solution of the differential equation \(x+y \frac{d y}{d x}=\sec \left(x^2+y^2\right)\) is

  1. A \(\sin \left(x^2+y^2\right)=2 x+c\)
  2. B \(\sin \left(x^2+y^2\right)+2 x=c\)
  3. C \(\sin \left(x^2+y^2\right)+x=c\)
  4. D \(\cos \left(x^2+y^2\right)=2 x+c\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(\sin \left(x^2+y^2\right)=2 x+c\)

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \text { We have, } x+y \frac{d y}{d x}=\sec \left(x^2+y^2\right) \\ & \text { Put } x^2+y^2=u \Rightarrow 2 x+2 y \frac{d y}{d x}=\frac{d u}{d x} \\ & \therefore x+y \frac{d y}{d x}=\frac{1}{2} \frac{d u}{d x} \\ & \therefore \frac{1}{2} \frac{d u}{d x}=\sec u \\ & \therefore \int \frac{d u}{\sec u}=\int 2 d x \\ & \therefore \sin u=2 x+c \\ & \Rightarrow \sin \left(x^2+y^2\right)=2 x+c\end{aligned}\)
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