The phase margin of a system with the open-loop transfer

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The phase margin of a system with the open-loop transfer function
G(s) H(s) = (1 - s) is
(1 + s)(2 + s)

1. 0°
2. 63.4°
3. 90°
4. ∞

Correct Option: D

| G(jω) H(jω)| ≠ 1, for any value of ω,
Therefore phase margin ∞ .