# de4 - Dierential Equations Test 4 Solutions Answer FOUR...

This preview shows pages 1–2. Sign up to view the full content.

Differential Equations Test 4 Solutions Answer FOUR questions. Show all working clearly. 1. Define the Laplace transform Y = L ( y ) of y . From the definition, calculate that if y ( t ) = te at then Y ( s ) = 1 / ( s - a ) 2 . 2. (i) Show that if y ( t ) has Laplace transform Y ( s ) then y ( t ) has Laplace transform sY ( s ) - y (0). (ii) Assuming that L (cos αt ) = s/ ( s 2 + α 2 ) (or otherwise) calculate L (sin αt ). 3. By Laplace transform methods, solve the initial value problem y + 2 y + y = 2 cos t ; y (0) = 0 , y (0) = 0 . 4. By Laplace transform methods, solve the initial value problem y + 4 y = 16 te - 2 t ; y (0) = 1 , y (0) = 0 . 5. Find a solution to the differential equation ty + y = 1 using Laplace transform methods. Notice that the differential equation does not have constant coefficients; recall that multiplication by - t corresponds to differentiation by s . Solutions : 1. By definition, Y ( s ) = 0 e - st y ( t )d t. When y ( t ) = te at it is plain that Y ( a ) is undefined, while if s = a then (integrating by parts) Y ( s ) = 0 te ( a - s ) t d t = te ( a - s ) t / ( a - s ) 0 - 0 { e ( a - s ) t / ( a - s ) } d t so that Y ( s ) = te ( a - s ) t / ( a - s ) - e ( a - s ) t / ( a - s ) 2 0 ;

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern