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For the differential equation (xlog⁡ex)dy=(log⁡ex−y)dx\left(x \log _{e} x\right) d y=\left(\log _{e} x-y\right) d x

(A) Degree of the given differential equation is 11.

(B) It is a homogeneous differential equation.

(C) Solution is 2ylog⁡ex+A=(log⁡ex)22y \log _{\mathrm{e}} \mathrm{x}+A=\left(\log _{\mathrm{e}} \mathrm{x}\right)^{2}, where AA is an arbitrary constant

(D) Solution is 2ylog⁡ex+A=log⁡e(log⁡ex)2 y \log _{e} x+A=\log _{e}\left(\log _{e} x\right), where AA is an arbitrary constant

Choose the correct answer from the options given below :

Solution

✅ Correct Option: 1

Option (A): Degree of the given differential equation is 1.

Rearranging the equation to standard form:

dydx=log⁡ex−yxlog⁡ex\dfrac{dy}{dx} = \dfrac{\log_e x - y}{x \log_e x}

Since dydx\dfrac{dy}{dx} has a power of 1, the degree is 1.

Option (A) is correct.


Option (B): It is a homogeneous differential equation.

A differential equation is homogeneous if f(tx,ty)=f(x,y)f(tx,ty) = f(x,y) for any non-zero t.

For our equation: f(x,y)=log⁡ex−yxlog⁡exf(x,y) = \dfrac{\log_e x - y}{x \log_e x}

Substituting (tx,ty)(tx,ty):

f(tx,ty)=log⁡e(tx)−tytxlog⁡e(tx)=log⁡et+log⁡ex−tytx(log⁡et+log⁡ex)f(tx,ty) = \dfrac{\log_e(tx) - ty}{tx \log_e(tx)} = \dfrac{\log_e t + \log_e x - ty}{tx(\log_e t + \log_e x)}

This is not equal to f(x,y)f(x,y) due to the log⁡et\log_e t terms.

Option (B) is incorrect.


Options (C) & (D): Solving the equation

Rearranging to group terms:

(xlog⁡ex)dy+y dx=log⁡ex dx(x \log_e x)dy + y\,dx = \log_e x\,dx

Let's define u=log⁡exu = \log_e x, which means du=dxxdu = \dfrac{dx}{x}.

Substituting, our equation becomes:

u dy+y du=u duu\,dy + y\,du = u\,du

This is the differential of the product uyuy:

d(uy)=u dy+y du=u dud(uy) = u\,dy + y\,du = u\,du

Integrating both sides:

uy=u22+Cuy = \dfrac{u^2}{2} + C

Substituting back u=log⁡exu = \log_e x:

ylog⁡ex=(log⁡ex)22+Cy \log_e x = \dfrac{(\log_e x)^2}{2} + C

Multiplying by 2:

2ylog⁡ex=(log⁡ex)2+2C2y \log_e x = (\log_e x)^2 + 2C

Let A=2CA = 2C, so:

2ylog⁡ex+A=(log⁡ex)22y \log_e x + A = (\log_e x)^2

Option (C) is correct, and Option (D) is incorrect.


The correct options are (A) and (C).

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