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JEE Advanced 2025Paper 2
Exam
JEE Advanced
Year
2025
Paper
Paper 2
Subject
Mathematics
Chapter
Differential Equations

JEE Advanced 2025 · Paper 2 · Mathematics · Differential Equations

Let y(x) be the solution of the differential equation x^2 (d y)/(d...

Let y(x)y(x) be the solution of the differential equation x2dydx+xy=x2+y2,x>1ex^2 \frac{d y}{d x}+x y=x^2+y^2, x>\frac{1}{e} satisfying y(1)=0y(1)=0. Then the value of $2 \frac{(y(e))^2}{y\left(e^2\right)} is _____ .

Correct answer

0

Step-by-step solution

Put y=vx⇒dydx=v+xdvdx\mathrm{y}=\mathrm{vx} \Rightarrow \frac{d y}{d x}=v+x \frac{d v}{d x} D.E. x2(v+x dvdx)+x2v=x2(1+v2)⇒v+xdvdx+v=1+v2⇒xdvdx=1+v2−2v⇒∫dv(v−1)2=∫dxx⇒−1v−1=ln⁡∣x∣+C\begin{aligned} & \mathrm{x}^2\left(v+\mathrm{x} \frac{\mathrm{~d} v}{\mathrm{dx}}\right)+\mathrm{x}^2 v=\mathrm{x}^2\left(1+v^2\right) \\ & \Rightarrow v+x \frac{d v}{d x}+v=1+v^2 \\ & \Rightarrow x \frac{d v}{d x}=1+v^2-2 v \\ & \Rightarrow \int \frac{d v}{(v-1)^2}=\int \frac{d x}{x} \\ & \Rightarrow-\frac{1}{v-1}=\ln |x|+\mathrm{C} \end{aligned}\Rightarrow \frac{\mathrm{x}}{\mathrm{x}-\mathrm{y}}=\ln |x|+\mathrm{C}=\ln \mathrm{x}+\mathrm{C} \quad(\left(\right. Since x>1e)\left.\mathrm{x}>\frac{1}{\mathrm{e}}\right) Given y(1)=0⇒C=1y(1)=0 \Rightarrow C=1 So xx−y=ln⁡(ex)\frac{x}{x-y}=\ln (e x) Now y(e)=e2y(e)=\frac{e}{2} and $y\left(e^2\right)=\frac{2 e^2}{3} \therefore \frac{2(y(e))^2}{y\left(e^2\right)}=\frac{2 \cdot \frac{e^2}{4}}{\frac{2 e^2}{3}}=\frac{3}{4}=0.75
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