例5试求取X(s)=k/s2(+a)的乙变换。 解: S1=0 2 S =-a r 2 x(Z)=R1+R2 R 1(2-(s-0)2 k S(S+a)z-e STo Is=0 =k=2+(a+1)z (z-1) 2=lim(s+a)2A s→-a S(5+a)z-e X(、D的。-x2+(mn+1+k (4 KzlaTo-1+e)z+(1-e at at aloe a2(z-1)2(Z-e0)a ( 1) ( ) KZ[(aT - 1 e ) (1 e e )] ( ) R lim ( ) R [ ( 0) ] X(Z) R R S -a r 1 n 2 S 0 r 2 0 0 0 0 2 2 0 0 2 2 0 2 0 2 2 0 2 2 0 2 2 2 -aT 0 -aT -aT 0 a k ( 1) ( 1) a k 1 2 a k ( ) 2 ( 1) ( 1) a k 0 ( ) 2 (2 1)! 1 1 1 2 2 1 a T z e z z z a T z z e z z e z s s a k s a z z a T z s z e z s s a k d s d Z Z e Z aT X Z R R s a s aT aT aT ST − − − − + + − →− + − − − + + = − + − − − + + − − = = + = + = = + = = − = + = = = = = − − − 例5.试求取X(s)=k/s2 (s+a)的Z变换。 解：