Mathematics · Differential Equations

JEE Advanced 2025 — Paper 1 — Question 27

For all x>0x>0, let y1(x),y2(x)y_{1}(x), y_{2}(x), and y3(x)y_{3}(x) be the functions satisfying \end{enumerate} dy1dx−(sin⁡x)2y1=0,y1(1)=5dy2dx−(cos⁡x)2y2=0,y2(1)=13dy3dx−(2−x3x3)y3=0,y3(1)=35e\begin{aligned} & \frac{d y_{1}}{d x}-(\sin x)^{2} y_{1}=0, y_{1}(1)=5 \\ & \frac{d y_{2}}{d x}-(\cos x)^{2} y_{2}=0, y_{2}(1)=\frac{1}{3} \\ & \frac{d y_{3}}{d x}-\left(\frac{2-x^{3}}{x^{3}}\right) y_{3}=0, y_{3}(1)=\frac{3}{5 e} \end{aligned}

respectively. Then lim⁡x→0+y1(x)y2(x)y3(x)+2xe3xsin⁡x\lim _{x \rightarrow 0^{+}} \frac{y_{1}(x) y_{2}(x) y_{3}(x)+2 x}{e^{3 x} \sin x} is equal to \qquad

Answer: 2

Numerical answer — enter this value.

Step-by-step solution

dy1y1+dy2y2+dy3y3=(sin⁡2x+cos⁡2x+2−x3x3)dx\quad \frac{d y_{1}}{y_{1}}+\frac{d y_{2}}{y_{2}}+\frac{d y_{3}}{y_{3}}=\left(\sin ^{2} x+\cos ^{2} x+\frac{2-x^{3}}{x^{3}}\right) d x

ln⁡(y1y2y3)=−1x2+C\ln \left(y_{1} y_{2} y_{3}\right)=\frac{-1}{x^{2}}+C

ln⁡(y1(x)y2(x)y3(x))=−1x2+C\ln \left(\mathrm{y}_{1}(\mathrm{x}) \mathrm{y}_{2}(\mathrm{x}) \mathrm{y}_{3}(\mathrm{x})\right)=\frac{-1}{\mathrm{x}^{2}}+\mathrm{C}

ln⁡(5⋅13⋅35e)=−1x2+C\ln \left(5 \cdot \frac{1}{3} \cdot \frac{3}{5 \mathrm{e}}\right)=\frac{-1}{\mathrm{x}^{2}}+\mathrm{C}

∴C=0\therefore \mathrm{C}=0

y1(x)y2(x)y3(x)=e−1x2y_{1}(x) y_{2}(x) y_{3}(x)=e^{\frac{-1}{x^{2}}}

lim⁡x→0e−1x2+2xe3xsin⁡x\lim _{x \rightarrow 0} \frac{e^{\frac{-1}{x^{2}}}+2 x}{e^{3 x} \sin x}

lim⁡x→01e3x+1x2sin⁡x+lim⁡x→02xe3xsin⁡x\lim _{x \rightarrow 0} \frac{1}{e^{3 x+\frac{1}{x^{2}}} \sin x}+\lim _{x \rightarrow 0} \frac{2 x}{e^{3 x} \sin x}

lim⁡x→01e3x⋅sin⁡xx⋅e1x21x+2\lim _{x \rightarrow 0} \frac{1}{e^{3 x} \cdot \frac{\sin x}{x} \cdot \frac{e^{\frac{1}{x^{2}}}}{\frac{1}{x}}}+2

=0+2{lim⁡y→∞ey2y=ey2⋅2y1=∞}=0+2 \quad\left\{\lim _{y \rightarrow \infty} \frac{e^{y^{2}}}{y}=\frac{e^{y^{2}} \cdot 2 y}{1}=\infty\right\}

=2=2

Answer key and solution verified before publishing.

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Exam
JEE Advanced 2025
Paper
Paper 1
Subject
Mathematics
Chapter
Differential Equations
Topic
Methods of solving a First Order,First Degree Differential