Explain with steps please

Find L-1 S 2a3 {+} (s + a) The function we wish to invert must be expressed in a form in which its inv form may be recognized. Thus, L-1 2a3 (s + a) = -1} a + a a a(s + a) a(s a) s-a2 (s + a2) (s + a2)2 } = sin(at) - a - { L-1 {- d S =sin(at) at cos(at). ds s a