Question

Use appropriate algebra and Theorem 7.2.1 to find the given inverse Laplace transform. (Write your answer as a function of t.)

(s + 1)3

Answer 1

Expand the expression as

(s + 1)³/s ⁵ = (s ³ + 3s ² + 3s + 1)/s ⁵

… = 1/s ² + 3/s ³ + 3/s ⁴ + 1/s ⁵

Then taking the inverse transform, you get

LT⁻¹ [1/s ² + 3/s ³ + 3/s ⁴ + 1/s ⁵]

… = LT⁻¹ [1/s ²] + LT⁻¹ [3/s ³] + LT⁻¹ [3/s ⁴] + LT⁻¹ [1/s ⁵]

… = LT⁻¹ [1!/s ²] + 3/2 LT⁻¹ [2!/s ³] + 1/2 LT⁻¹ [3!/s ⁴] + 1/24 LT⁻¹ [4!/s ⁵]

… = t + 3/2 t ² + 1/2 t ³ + 1/24 t ⁴