Thread: laplace transform(t^2cos(t))=

= (-1)^2 (d^2/ds^2) laplace(cos(t))

= (d^2/ds^2) (s/(s^2+1))

= (d/ds) [-2s^2(s^2+1)^-2 + (s^2+1)^-1]

= 8s^3/ (s^2+1)^3 - 6s/(s^2+1)^2

thats the answer i got but the answer in the book says (2s^3 - 6s)/ (s^2+1)^3

where did i go wrong?

Originally Posted by linalg123

= (-1)^2 (d^2/ds^2) laplace(cos(t))

= (d^2/ds^2) (s/(s^2+1))

= (d/ds) [-2s^2(s^2+1)^-2 + (s^2+1)^-1]

= 8s^3/ (s^2+1)^3 - 6s/(s^2+1)^2

thats the answer i got but the answer in the book says (2s^3 - 6s)/ (s^2+1)^3

where did i go wrong?

You didn't go wrong anywhere!! Just combine the two fractions you got to get the desired result!!

ughh..duhhh.. thanks