Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Differential Equations

Question:

I.F. for y ln y $\frac{dx}{dy}$ + x − ln y = 0 is :

Options:

ln x

ln y

ln xy

none of these

Correct Answer:

ln y

Explanation:

The correct answer is Option (2) → $ln\, y$

$y\, ln\, y\frac{dx}{dy} + x - ln\, y = 0$

$⇒y\, ln\, y\frac{dx}{dy} + x=ln\, y$

$⇒\frac{dx}{dy}+\frac{1}{y\, ln\, y}+x=\frac{1}{y}$

$I.F.=e^{\int P\,dy}$

$=e^{\int \frac{1}{y\, ln\, y}dy}$

$=e^{ln|ln\,y|}=ln\,y$