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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
(x-50000)/x = 0.45 // - 0.45
(x-50000)/x-0.45 = 0
(x-50000)/x+(-0.45*x)/x = 0
x-0.45*x-50000 = 0
0.55*x-50000 = 0
(0.55*x-50000)/x = 0
(0.55*x-50000)/x = 0 // * x
0.55*x-50000 = 0
0.55*x-50000 = 0 // + 50000
0.55*x = 50000 // : 0.55
x = 50000/0.55
x = 90909.09090909
x = 90909.09090909
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