Examples,Ogata,pp.278 s3+2s2+s+2=(s2+1)(s+2)=0 s3 1 s4+2s3+3s2+6s+1=0 s2 2 2 s 0 0 A pair of imaginary roots 2 s3-3s+2=(s-1)2(s+2)=0 1 -3 s2 0≈8 2 -3 2 0 →One sign change → 2 One sign change2 0 0 0 2 2 1 1 0 1 2 3 s s s s      32 2 s ss s s       2 2 1 20 Examples, Ogata, pp.278 2 0 0 2 3 0 2 1 3 0 1 2 3 s s s s       A pair of imaginary roots One sign change One sign change 2 3 6 1 0 4 3 2 s  s  s  s   3 2 ss s s      3 2 ( 1) ( 2) 0