GATE 2026 EC – Question 59
Consider the unity negative feedback control system shown in the Figure. The value of gain $K\,(>0)$ at which the given system will remain marginally stable is ________. (Answer in integer)
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Correct answer: 1386
Explanation
The characteristic equation is $s^3+18s^2+77s+K=0$. By Routh, marginal stability occurs when $18\times77=K$, so $K=1386$.