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D( x )
x+500 = 0
x+500 = 0
x+500 = 0
x+500 = 0 // - 500
x = -500
x in (-oo:-500) U (-500:+oo)
x/(x+500) = 0.25 // - 0.25
x/(x+500)-0.25 = 0
x/(x+500)+(-0.25*(x+500))/(x+500) = 0
x-0.25*(x+500) = 0
0.75*x-125 = 0
(0.75*x-125)/(x+500) = 0
(0.75*x-125)/(x+500) = 0 // * x+500
0.75*x-125 = 0
0.75*x-125 = 0 // + 125
0.75*x = 125 // : 0.75
x = 125/0.75
x = 166.66666667
x = 166.66666667
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