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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
(x-0.65)/x = 0.25 // - 0.25
(x-0.65)/x-0.25 = 0
(x-0.65)/x+(-0.25*x)/x = 0
x-0.25*x-0.65 = 0
0.75*x-0.65 = 0
(0.75*x-0.65)/x = 0
(0.75*x-0.65)/x = 0 // * x
0.75*x-0.65 = 0
0.75*x-0.65 = 0 // + 0.65
0.75*x = 0.65 // : 0.75
x = 0.65/0.75
x = 0.86666667
x = 0.86666667
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