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 solution of the differential equation $x dy - y dx = \sqrt{x^2+y^2} dx$, given that $y=1$ when $x=\sqrt{3}$, is

If $y' = \frac{x - y}{x + y}$,then its solution is

If $y \frac{dy}{dx} = x \left[ \frac{y^2}{x^2} + \frac{\phi(y^2/x^2)}{\phi'(y^2/x^2)} \right]$,$x > 0$,$\phi > 0$,and $y(1) = -1$,then $\phi(y^2/4)$ is equal to:

Find the particular solution satisfying the given condition:
$x^{2} dy + (xy + y^{2}) dx = 0$; $y = 1$ where $x = 1$.

Difficult
View Solution

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

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