How to reduce?

  • Thread starter yukcream
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How to reduce the equation: Show how the equation u(t)+Int( 0->t) {[e^a(t-t1)]u(t1)}dt1 = k can be reduced to a differential equation and obtain an intial condidtion for the equation.

Remarks: Int(0->t): integral from 0 to t !
 

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  • #2
arildno
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Evaluate your equation at t=0. What does that say about u(0)?

Differentiate your equation to get your differential equation.
 
  • #3
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arildno said:
Evaluate your equation at t=0. What does that say about u(0)?

Differentiate your equation to get your differential equation.
Yes I know I have to differential but if the diff. it with respect to t , what will happen to the second term on the left hand side?
 
  • #4
lurflurf
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yukcream said:
Yes I know I have to differential but if the diff. it with respect to t , what will happen to the second term on the left hand side?
Use the Leibniz Integral Rule.
[tex]\frac{d}{dt}\int_{a(t)}^{b(t)}f(x,t)dx=\int_{a(t)}^{b(t)}
\partial_tf(x,t)dx+f(x,t)\partial_tx|_{x=a(t)}^{x=b(t)}[/tex]
[tex]\frac{d}{dt}\int_{a(t)}^{b(t)}f(x,t)dx=\int_{a(t)}^{b(t)}
\frac{\partial}{\partial t}f(x,t)dx+f(x,t){\partial x}{\partial t}\right|_{x=a(t)}^{x=b(t)}[/tex]
http://mathworld.wolfram.com/LeibnizIntegralRule.html
for the initial condition you should know that
[tex]\int_0^0 f(x) dx=0[/tex]
 
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