In Routh-Hurwitz stability criterion, the number of roots of the characteristic equation lying in the right half of the s-plane equals:
ANumber of sign changes in the first column of Routh array
BNumber of zero elements in second column
CNumber of rows in Routh array
DTotal degree of characteristic polynomial plus one
Explanation
The number of sign changes in the first column of the Routh array strictly equals the number of unstable roots in the right-half s-plane.

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