Question

For the function F (s) = (s^2+s+1)/s(s+5)(s+3), after splitting this function into partial fractions, co-efficient of 1/(s+3) is?

(a) -1.17

(b) 1.17

(c) -2.27

(d) 2.27

The question was posed to me at a job interview.

This intriguing question comes from Inverse Transforms in portion Intoduction to the Laplace Transform of Network Theory

Answer 1

The correct choice is (a) -1.17

Best explanation: To obtain the constant C, multiply the given equation with (s+3) and putting s = -3. C = (s + 3)F (s)|s = -3 = (s^2+s+1)/s(s+5)|s=-3 = -1.17.