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JEE Advanced 2011Paper 2
Exam
JEE Advanced
Year
2011
Paper
Paper 2
Subject
Mathematics
Chapter
Differential Equations

JEE Advanced 2011 · Paper 2 · Mathematics · Differential Equations

Let y^ (x)+y(x) g^ (x)=g(x) g^ (x) y(0)=0, x ∈ R , where f^ (x)...

Let y′(x)+y(x)g′(x)=g(x)g′(x)y(0)=0,x∈Ry^{\prime}(x)+y(x) g^{\prime}(x)=g(x) g^{\prime}(x) y(0)=0, x \in R, where f′(x)f^{\prime}(x) denotes df(x)dx\frac{d f(x)}{d x} and g(x)g(x) is a given non-constant differentiable function on RR with g(0)=g(2)=0g(0)=g(2)=0. Then, the value of yy (2) is...

Correct answer

0

Step-by-step solution

\frac{d y}{d x}+y \cdot g^{\prime}(x)=g(x) g^{\prime}(x)\mathrm{IF}=e\intg′(x)dx=eg(x)e^{\intg^{\prime}(x) d x}=e^{g(x)}\thereforeSolutionisySolution is y\left(e^{g(x)}\right)=\intg(x)g(x)\cdotg′(x)g^{\prime}(x)\cdoteg(x)dx+CPute^{g(x)} d x+C Putg(x)=t, g^{\prime}(x) d x=d ty(eg(x))=\intt\cdotetdt+C=t\cdotet−∫1\cdotetdt+C=t\cdotet−et+Cyeg(x)=(g(x)−1)eg(x)+C…(i)\begin{aligned}& y\left(e^{g(x)}\right)=\intt \cdote^t d t+C \\ = & t \cdote^t-\int1 \cdote^t d t+C=t \cdote^t-e^t+C \\ & y e^{g(x)}=(g(x)-1) e^{g(x)}+C \quad \ldots(\mathrm{i}) \end{aligned}Given,Given,y(0)=0, g(0)=g(2)=0\thereforeEq.(i)becomes,Eq. (i) becomes,y(0)\cdoteg(0)=(g(0)−1)\cdoteg(0)+C⇒0=(−1)⋅1+C⇒C=1∴y(x)\cdoteg(x)=(g(x)−1)eg(x)+1⇒y(2)\cdoteg(2)=(g(2)−1)eg(2)+1 where, \quadg(2)=0⇒y(2)⋅1=(−1)⋅1+1⇒y(2)=0\begin{aligned}& \quad y(0) \cdote^{g(0)}=(g(0)-1) \cdote^{g(0)}+C \\ & \Rightarrow \quad 0=(-1) \cdot1+C \Rightarrow C=1 \\ & \therefore \quad y(x) \cdote^{g(x)}=(g(x)-1) e^{g(x)}+1 \\ & \Rightarrow \quad y(2) \cdote^{g(2)}=(g(2)-1) e^{g(2)}+1 \\ & \text{ where, } \quadg(2)=0 \\ & \Rightarrow \quad y(2) \cdot1=(-1) \cdot1+1 \Rightarrow y(2)=0 \end{aligned}$
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