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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
(89-x)/x = -0.04 // + 0.04
(89-x)/x+0.04 = 0
(89-x)/x+(0.04*x)/x = 0
0.04*x-x+89 = 0
89-0.96*x = 0
(89-0.96*x)/x = 0
(89-0.96*x)/x = 0 // * x
89-0.96*x = 0
89-0.96*x = 0 // - 89
-0.96*x = -89 // : -0.96
x = -89/(-0.96)
x = 92.70833333
x = 92.70833333
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