The necessary condition for the stability of the linear system is that all the coefficients of characteristic equation 1+G(s)H(s) =0, be real and have the :

The necessary condition for the stability of the linear system is that

1.	The necessary condition for the stability of the linear system is that all the coefficients of characteristic equation 1+G(s)H(s) =0, be real and have the :
A.	Positive sign
B.	Negative sign
C.	Same sign
D.	Both positive and negative
Answer» D. Both positive and negative