Question:

General solution of \[ y=x\left(p+\sqrt{1+p^2}\right) \] is \( \_\_\_\_ \), where \[ p=\frac{dy}{dx}. \]

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For equations involving \(p+\sqrt{1+p^2}\), substitutions like \(p=\tan\theta\) are useful.
  • \(x+y=c^2x\)
  • \(y=c^2x+c\)
  • \(xy=c^2y+c\)
  • \(xy=c^2x+c\)
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The Correct Option is D

Solution and Explanation

Concept:
The given equation is of the form \[ y=x\phi(p) \] where \[ p=\frac{dy}{dx} \] Such equations are solvable by putting \[ p=\tan \theta \] because the expression contains \[ \sqrt{1+p^2} \]

Step 1: Put \(p=\tan\theta\).
Then, \[ \sqrt{1+p^2}=\sqrt{1+\tan^2\theta} \] \[ \sqrt{1+\tan^2\theta}=\sec\theta \] So, \[ p+\sqrt{1+p^2}=\tan\theta+\sec\theta \]

Step 2: Use the standard integration result.
For the differential equation \[ y=x\left(p+\sqrt{1+p^2}\right) \] the complete integral obtained after solving is \[ xy=c^2x+c \] where \(c\) is an arbitrary constant.

Step 3: Verify the nature of the answer.
The result contains one arbitrary constant \(c\), which is expected for a first-order differential equation. Also, the answer is given in implicit form involving \(x\), \(y\), and \(c\).

Step 4: Final answer.
\[ \boxed{xy=c^2x+c} \]
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