Show that the differential equation $x^{2} \frac{dy}{dx} = x^{2} + xy - 2y^{2}$ is a homogeneous equation and find its general solution.

Vedclass pdf generator app on play store
Vedclass iOS app on app store
(N/A) The given differential equation is $x^{2} \frac{dy}{dx} = x^{2} + xy - 2y^{2}$.
$\frac{dy}{dx} = \frac{x^{2} + xy - 2y^{2}}{x^{2}}$.
Let $F(x, y) = \frac{x^{2} + xy - 2y^{2}}{x^{2}}$.
$F(\lambda x, \lambda y) = \frac{(\lambda x)^{2} + (\lambda x)(\lambda y) - 2(\lambda y)^{2}}{(\lambda x)^{2}} = \frac{\lambda^{2}(x^{2} + xy - 2y^{2})}{\lambda^{2}x^{2}} = \lambda^{0} F(x, y)$.
Since $F(\lambda x, \lambda y) = \lambda^{0} F(x, y)$,the given differential equation is a homogeneous equation.
To solve it,substitute $y = vx$,which implies $\frac{dy}{dx} = v + x \frac{dv}{dx}$.
Substituting these into the equation:
$v + x \frac{dv}{dx} = \frac{x^{2} + x(vx) - 2(vx)^{2}}{x^{2}} = 1 + v - 2v^{2}$.
$x \frac{dv}{dx} = 1 - 2v^{2}$.
$\frac{dv}{1 - 2v^{2}} = \frac{dx}{x}$.
$\frac{1}{2} \int \frac{dv}{(\frac{1}{\sqrt{2}})^{2} - v^{2}} = \int \frac{dx}{x}$.
Using the formula $\int \frac{dx}{a^{2} - x^{2}} = \frac{1}{2a} \log |\frac{a+x}{a-x}| + C$:
$\frac{1}{2} \cdot \frac{1}{2(1/\sqrt{2})} \log |\frac{1/\sqrt{2} + v}{1/\sqrt{2} - v}| = \log |x| + C$.
$\frac{1}{2\sqrt{2}} \log |\frac{1 + \sqrt{2}v}{1 - \sqrt{2}v}| = \log |x| + C$.
Substituting $v = \frac{y}{x}$:
$\frac{1}{2\sqrt{2}} \log |\frac{x + \sqrt{2}y}{x - \sqrt{2}y}| = \log |x| + C$.

Explore More

Similar Questions

The general solution of $x \frac{dy}{dx} = y - x \tan \left( \frac{y}{x} \right)$ is . . . . . .

The general solution of the differential equation $x^2 dy - (xy - y^2) dx = 0$ is

The general solution of the differential equation $(xy + y^2) dx - (x^2 - 2xy) dy = 0$ is

The general solution of the differential equation $x \cos \frac{y}{x}(y d x+x d y)=y \sin \frac{y}{x}(x d y-y d x)$ is

Let $y=y(x)$ be the solution of the differential equation $\left((x+2) e^{\left(\frac{y+1}{x+2}\right)}+(y+1)\right) d x=(x+2) d y$ with the initial condition $y(1)=1$. If the domain of $y=y(x)$ is an open interval $(\alpha, \beta)$,then $|\alpha+\beta|$ is equal to $......$

Vedclass Products

For Students

Vedclass Test Series

Mock tests in real JEE/NEET style with performance analysis. 5-day free trial.

Start Free Trial
For Teachers

Exam Paper Generator

Generate Set A/B/C/D exam papers from 7.5L+ questions in 2 minutes. 3 chapters free.

Try Free
For Institutes

Online Exam Module

Live online exams with unlimited students, 360° analytics & white-label branding.

See Demo