The differential equation of family of parabolas with focus at origin and \(\mathrm{x}\) -axis as axis is: (A) \(\mathrm{y}(\mathrm{dy} / \mathrm{dx})^{2}-2 \mathrm{x}(\mathrm{dy} / \mathrm{dx})=\mathrm{y}\) (B) \(\mathrm{y}(\mathrm{dy} / \mathrm{dx})^{2}+2 \mathrm{xy}(\mathrm{dy} / \mathrm{dx})=\mathrm{y}\) (C) \(\mathrm{y}(\mathrm{dy} / \mathrm{dx})^{2}-2 \mathrm{xy}(\mathrm{dy} / \mathrm{dx})=\mathrm{y}\) (D) \(\mathrm{y}(\mathrm{dy} / \mathrm{dx})^{2}+2 \mathrm{x}(\mathrm{dy} / \mathrm{dx})=\mathrm{y}\)

Short Answer

Expert verified
The short answer is: (A) \(y\left(\frac{dy}{dx}\right)^2 -2x\frac{dy}{dx} = y\).

Step by step solution

01

Write a general equation for the parabolas

The general equation of a parabola with its focus at (0, 0), and x-axis as the axis is given by: \[ x^2 = 4ay \]
02

Differentiate the equation with respect to x

Let's differentiate both sides of the equation \( x^2 = 4ay \) with respect to x to get: \[ 2x = 4a \frac{dy}{dx} \]
03

Solve for 'a'

We can solve for 'a' from the above equation, in terms of the derivative \(\frac{dy}{dx}\): \[ a = \frac{x}{2}\frac{dx}{dy} \]
04

Replace 'a' in the original equation

Substitute the value of 'a' into the original equation \( x^2 = 4ay \): \[ x^2 = 4\left(\frac{x}{2}\frac{dx}{dy}\right)y \]
05

Simplify the equation to obtain the differential equation

Simplifying the above equation yields: \[ x^2 = 2xy\frac{dy}{dx} \] Now, we need to rearrange the equation to get it in a form similar to the given options: \[ y\left(\frac{dy}{dx}\right)^2 -2x\frac{dy}{dx} = y \] This differential equation matches option (A), so the correct answer is: (A) \(y\left(\frac{dy}{dx}\right)^2 -2x\frac{dy}{dx} = y\)

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