# Need help with finding particular solution to a second order differential equation

1. Nov 10, 2009

### wshfulthinker

1. The problem statement, all variables and given/known data
Consider the differential equation:
y''+10y'+25y= f(x)

Find a particular solution if f(x) = 32xe^(-x)

2. Relevant equations
I already did the general solution when f(x)=0 and that is Ae^(-5x) + Bxe^(-5x)

3. The attempt at a solution
I tried yp=axe^(-x) and got a= 4x+2 which is wrong

does anyone know what particular solution i can try in order to get the answer?

Thanks

2. Nov 10, 2009

### Staff: Mentor

Re: Need help with finding particular solution to a second order differential equatio

If f(x) had been 32e-x, you would want to try yp = Ae-x. Since f(x) = 32xe-x, you want your particular solution to be yp = Ae-x + Bxe-x.

If f(x) had been 32x2e-x, you would try a particular solution of the form yp = Ae-x + Bxe-x + Cx2e-x. There's a reason for all of this, but I'll leave that for your instructor.

BTW, this is hardly a Precalculus question. You should have posted it in Calculus and Beyond.

3. Nov 10, 2009

### wshfulthinker

Re: Need help with finding particular solution to a second order differential equatio

Hi, thankyou so much for your reply. I tried it and it worked!!! i shall write it down and remember that forever now!

Also, sorry about posting in the wrong section! I can't believe i did that because i took so long to check that my post was right.. i guess i forgot to check if i had clicked on the right section..! Thankyou so much though.

4. Nov 10, 2009

### HallsofIvy

Re: Need help with finding particular solution to a second order differential equatio

Generally speaking when a "right hand side" involves an $n^{th}$ power of x, you should try a polynomial of degree n down.