Question

show L^-1(s^3/s^4 + 4a^4) = coshatcosat haha

Answer 1

so s^4 + 4a^2 = (s^2 - 2as + 2a^2)(s^2 + 2as + 2a^2)

Answer 2

http://www.wolframalpha.com/input/?i=L^-1%28s^3%2F%28s^4+%2B+4a^4%29%29

Answer 3

i don't think you can factorize that way. there is 'i' involved. factorize s^4 + 4a^4 as (s^2 + i2a^2)(s^2 - i2a^2) and use convolution.