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the differential equation is :

$$\frac{dy}{dx}+y=f(x),~~~~~~~~ y(0)=0$$

where,

$$f(x)=\cases{2,& if $0\le x\lt1$\\0,& if $x\ge 1$}.$$

So what i did was....

since it is a linear differential equation, i calculated its I.F(integrating factor)= $e^x$

and used..

$$y(I.F)=\int (e^x f(x)+c\tag{1})\,dx.$$

Now, how should i use the splitting of $f(x)$ to solve for $y$ in $(1)$

Please help

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  • $\begingroup$ Another approach is Laplace transforms. $\endgroup$ – Amzoti Jan 17 '15 at 15:17
  • $\begingroup$ @Amzoti i have no idea of that, i'll look into it for sure. $\endgroup$ – Shobhit Jan 17 '15 at 15:21
  • $\begingroup$ write up two solution in the different range and match them at the boundary by requiring $y$ to be continuous. the derivative will certainly have a jump. $\endgroup$ – abel Jan 20 '15 at 16:29
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solving for $y$ in the interval $[0,1],$ you find $y = 2 -2 e^{-x}$ and $y(1) = 2 - 2/e.$ use this as the initial value and solve $\dfrac{dy}{dx} + y = 0$ to get $y = 2(e-1)e^{-x}$ for $x \ge 1$.

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  • $\begingroup$ oh yeah, got it. thnks $\endgroup$ – Shobhit Jan 22 '15 at 15:10

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