The forward-path transfer function of a unity feedback system

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The forward-path transfer function of a unity feedback system is
G(s) = K(s² - 4)
s³ + 3

For the system to be stable the range of K is

1. K > -1
2. K < 3
  4
3. -1 < K < 3
  4
4. marginal stable

Correct Option: D

Closed loop transfer function

T(s) =	K(s² - 4)
	(K + 1)s² + (3 - 4K)

The system can be only marginally stable.