Question:

The curve for which the length of the normal is equal to the length of the radius vector, are

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Set up the differential equation and solve for the family of curves.
Updated On: Apr 23, 2026
  • only circles
  • only rectangular hyperbolas
  • either circles or rectangular hyperbolas
  • None of the above
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The Correct Option is C

Solution and Explanation

Step 1: Formula / Definition}
\[ \text{Normal length} = y\sqrt{1 + \left(\frac{dy}{dx}\right)^2}, \text{Radius vector} = \sqrt{x^2 + y^2} \]
Step 2: Calculation / Simplification}
\(y^2\left[1 + \left(\frac{dy}{dx}\right)^2\right] = x^2 + y^2\)
\(y^2\left(\frac{dy}{dx}\right)^2 = x^2 \Rightarrow \frac{dy}{dx} = \pm \frac{x}{y}\)
\(y dy = \pm x dx \Rightarrow \frac{y^2}{2} = \pm \frac{x^2}{2} + c\)
\(x^2 + y^2 = c_1\) (circles) or \(x^2 - y^2 = c_2\) (rectangular hyperbolas)
Step 3: Final Answer
\[ \text{either circles or rectangular hyperbolas} \]
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