# laplace help

• Aug 13th 2010, 01:11 AM
aussieiron86
laplace help
hey guys,

not too sure if this is the right area, but i have 2 maths problems that i am struggling with. Does anyone know how to do these two laplace questions?

i have already tried once and failed and i only get one more attempt on the online test

Find laplace of

d^2y/dt^t-13dy/dt+42y=6e^(-4t)
y(0)=0
y'(0)=3

and find the solution of the integral using laplace

f(t)=5+3t^2+2{f(u)sin(2(t-u))

the { is meant to be the integral sign

Thanks
• Aug 13th 2010, 02:01 AM
roshanhero
Apply laplace transform on both sides.
• Aug 13th 2010, 02:36 AM
aussieiron86
i answered the first one but i keep getting the second one wrong any chance of some help
• Aug 13th 2010, 02:51 AM
Ackbeet
You can find the LT of the first DE using the standard tables and theorems. The initial conditions get included when you take the LT of derivatives. As for the second equation, the integral there is a convolution, which transforms in a particularly nice fashion. I think you meant to say, "Find the solution of the integral equation using Laplace...", right?

So, what do you get when you apply these techniques?
• Aug 13th 2010, 03:10 AM
aussieiron86
thanks ackbeet,

i know the first section will be 5/s+6/s^3+2/S then the laplce of the next is 2/s^2-4,

i am just confused as to where to go from here, we didnt do any examples of this in class and it has just popped up on the online test
• Aug 13th 2010, 03:28 AM
aussieiron86
Can someoe please help it is only open for another 1 1/2 hours and this is the only question i have left and i will be done with Laplace for the semester
• Aug 13th 2010, 04:34 AM
Ackbeet
Hmm. You didn't mention before that this problem was on an online test. It's forum policy not knowingly to help with problems that count towards a grade.
• Aug 13th 2010, 05:19 AM
mr fantastic
Quote:

Originally Posted by Ackbeet
Hmm. You didn't mention before that this problem was on an online test. It's forum policy not knowingly to help with problems that count towards a grade.