The substitution $x=v y$ converts which one of the following differential equation to an equation solvabie…

The substitution $x=v y$ converts which one of the following differential equation to an equation solvabie by variable separable method?
  1. $\left(y^2-2 x^2 y\right) d x=\left(x^2-2 x y^2\right) d y$
  2. $x^2 d y-y d x=\sqrt{x^2+y^2} d x$
  3. $\frac{d y}{d x}=\frac{y^2}{x+\sqrt{x y}}$
  4. $\left(1+2 e^{\frac{x}{y}}\right)+2 e^{\frac{x}{y}}\left(1-\frac{x}{y}\right) \frac{d y}{d x}=0$

Solution

$x=v y$ converts those differential equation to variable separable form which we have Homogenous function $f(x, y)=\frac{d y}{d x}$ of order zero ie each term should have equal power. $\therefore$ Option (a) \& (b) are not homogeneous. Hence they are incorrect option. Option (c) have homogeneus function of order 1 because $\frac{d y}{d x}=\frac{y^2}{x+\sqrt{x y}}=f(x, y)$. Hence option (c) is also not correct. Option (d) is correct because it have homogenous function of order zero $\frac{d y}{d n}=f(x, y)=\frac{-\left(1+2 e^{\frac{x}{y}}\right)}{2 e^{\frac{x}{y}}\left(1-\frac{x}{y}\right)}$

Asked in: AP EAMCET 2023 (15 May Shift 1)

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