Problem 67
Find the general integral of the equation y'=(y)/(2yln y+y-x)
Find the general integral of the equation $y'=\dfrac{y}{2y\ln y+y-x}$.
Explanation of Method
Invert to treat $x$ as a function of $y$: $\dfrac{dx}{dy}=\dfrac{2y\ln y+y-x}{y}$ rearranges to a linear equation in $x$.
Step 1: Invert and rearrange
$\dfrac{dx}{dy}=2\ln y+1-\dfrac{x}{y}$, i.e. $\dfrac{dx}{dy}+\dfrac{x}{y}=2\ln y+1$.
Step 2: Apply the integrating factor
With $\mu(y)=e^{\int dy/y}=y$: $\dfrac{d}{dy}(xy)=2y\ln y+y$.
Step 3: Integrate
By parts, $\displaystyle\int 2y\ln y\,dy=y^2\ln y-\frac{y^2}{2}$, so $xy=y^2\ln y-\dfrac{y^2}{2}+\dfrac{y^2}{2}+C=y^2\ln y+C$.
Result
Final answer:
\[\boxed{\,xy=y^2\ln y+C,\qquad C\in\mathbb{R}}\]