![](https://cos-cdn.shuashuati.com/pipixue-web/2020-1231-2005-12/ti_inject-812ce.png)
If locus of G(jω)H(jω) passes through –1+j0 point, then zeros are not located on the jω axis; then we can see as, This is not desirable for practical control systems; For a well-designed closed-loop system, none of roots of characteristic equation should lie on jω axis.