Applying Partial Fractions to Solve Laplace Step Function Problems

myusernameis
Messages
56
Reaction score
0
step function - laplace...

Homework Statement


y"+y = f(t)

f(t) = 1, t<pi/2
0, pi/2<=t<infinity

The Attempt at a Solution



i now have L{y} = \frac{1-e^(-(pi/2)s)+s}{s(s^2+1)}

but how do i separate them and finish the problem?

thanks
 
Physics news on Phys.org


Use partial fractions like always.
\frac{1}{s(s^2+ 1)}= \frac{A}{s}+ \frac{Bs+ C}{s^2+ 1}

Find A, B, and C.
 


HallsofIvy said:
Use partial fractions like always.
\frac{1}{s(s^2+ 1)}= \frac{A}{s}+ \frac{Bs+ C}{s^2+ 1}

Find A, B, and C.

so no i have f(t) = 1-cos(t)+sin(t) - L{\frac{e^(pi*t/2)}{s(s^2+1)}}

how do i get the last laplace?
 
Last edited:
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top