()The roots of D(s)are equal In D(s) there are factors(S-P1 F(ky、+k2+ (s-p1)(s-n1)2a(s-p1) k1=(s-P1)2F(s) k12 (s-P1)2F(s S= PI S=PI (m-1)!ds m-(s-p1)"F(s) f(t)=k12e+knte+∑ken i=2 n-1 e pIt (s+a)"(m-1)!(3)The roots of D(s) are equal: In D(s) there are factors (s-p1 ) 2 . = − + − + − = n i i i s p k s p k s p k F s 2 2 1 11 1 12 ( ) ( ) ( ) ( ) 1 2 11 1 ( ) ( ) s p k s p F s = = −   1 2 1 2 1 ( ) ( ) s p s p F s ds d k = = −   1 1 1 1 1 ( ) ( ) ( 1)! 1 s p s p F s ds d m k m m m m = − − = − − } ( ) ( 1)! 1 { 1 1 p t m m e m t s −  + −  = = + + n i p t i p t p t i f (t ) k e k t e k e 2 1 2 1 1 1 1