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D( z )
z = 0
z = 0
z = 0
z in (-oo:0) U (0:+oo)
21.3/11.5 = 9.6/z // - 9.6/z
21.3/11.5-(9.6/z) = 0
21.3/11.5-9.6*z^-1 = 0
-9.6*z^-1 = -1.85217391 // : -9.6
z^-1 = 0.19293478
-1 < 0
1/(z^1) = 0.19293478 // * z^1
1 = 0.19293478*z^1 // : 0.19293478
5.18309866 = z^1
z = 5.18309866
z = 5.18309866
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