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The feedback control system shown in the figure is stable
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- for all K ≥ 0
- only if K ≥ 1
- only if 0 ≤ K < 1
- only if 0 ≤ K ≤ 1
Correct Option: C
Characteristic equation is
(K + 1) s2 + s(4 – 4K) +4 + 4 K = 0
Routh array drawn below,
| s2 | K + 1 | 4 (1 + K) |
| s | 4 (1 – K) | 0 |
For stability, coefficient in the first column is greater then zero, i.e. +ve
K + 1 > 0
1 > K and K ≥ 0.
