# Electronics and Communication Engineering - Automatic Control Systems - Discussion

Discussion Forum : Automatic Control Systems - Section 2 (Q.No. 1)
1.
The first column of a Routh array is

How many roots of the corresponding characteristic equation are in left half s-plane?
2
3
4
5
Explanation:

Total number of roots is 5. Since two sign changes in first column, two roots are in right half plane.

Hence 3 roots in left half plane.

Discussion:
5 comments Page 1 of 1.

RISHI NIGAM said:   2 years ago
Yes, it's three as total poles are 5 and two are in right, so 3 are in left.

Aishwarya said:   5 years ago
There are only two sign changes hence 2 roots in the left half of s-plane the how option B is correct can you explain it in detail?

Deswal said:   6 years ago
Highest power of s in characteristic equation decides the no of roots. Here it is 5. Also, sign change one time from positive to negative and then again from negative to positive hence it will change twice. So 5-2 =3 is equal to left half poles.

Priya said:   7 years ago
I think it is wrong, because in the routh array there is only one sign change.

Pardeep kumar said:   8 years ago
How we came to know the number of roots? Please explain.