Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Differential Equations

Question:

If $x\frac{dy}{dx}=y(\log y-\log x + 1)$ then the solution of the equation is:

Options:

$\log \frac{x}{y}=cy$

$\log \frac{y}{x}=cy$

$\log \frac{x^2}{y}=cy$

$\log \frac{y}{x}=cx$

Correct Answer:

$\log \frac{y}{x}=cx$

Explanation:

$x\,dy-y\,dx=y\log(\frac{y}{x})dx⇒\frac{x\,dy-y\,dx}{x^2}=\frac{y}{x}.\log(\frac{y}{x}).\frac{dx}{x}⇒\frac{d(\frac{y}{x})}{(\frac{y}{x})\log(\frac{y}{x})}=\frac{dy}{x}$

Substitute $\log (\frac{y}{x})=t⇒\log (\frac{y}{x})=cx$