Help solving a second order ODE with repeated roots, !

  • Thread starter adam640
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  • #1
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Help solving a second order ODE with repeated roots, urgent!

I have a differential equaition

d2y/dx2 - 6dy/dx + 9y = 0

I have found the general solution to be

y = (Ax + B)e3x

Now I need to find the solutions to A and B so that...

when y = 4, x = 0
when y = 49.e15, x = 5

I literally have no idea where to start with this question and I have this and a few others of a similar format due in a couple of hours, so any help is greatly appreciated. I understand the other methods for ODE's but I do not have any notes for this method and have been unable to find any resources online.

Any help is greatly appreciated!!!

Thanks,

Adam
 

Answers and Replies

  • #2
ehild
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Plug in y=4, x=0. You get an equation for the unknowns A and B. Then plug in y=49 e15, x=5 (simplify, do not evaluate!) It is an other equation for A, B. Two equations for two unknowns. Solve.

ehild
 
  • #3
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Thanks... I didn't think it would be that simple! I was going far too deep into this question.

It's been a long night! haha
 
  • #4
ehild
Homework Helper
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Maths is simpler than you imagine:smile:

ehild
 

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