Automatic Control Systems
If any term in the first column of a Routh array becomes zero, then

Routh criterion can be used by substituting a small positive number for zero and completing the array
Routh criterion can be used by substituting a small negative number for zero and complet-ing the array
Routh criterion can be used by substituting a big positive number for zero and completing the array
Routh criterion cannot be used to determine stability

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Automatic Control Systems
Which of the following features is not associated with Nichols chart?

The frequency at intersection of G(j?) locus and M = +3 dB locus gives bandwidth of closed loop system
(0 dB, -180°) point on Nichols chart represent critical Point (-1, 0)
It is symmetric about -180°
M loci are centred about (0 dB, -180°) point

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