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D( x )
x+670 = 0
x+670 = 0
x+670 = 0
x+670 = 0 // - 670
x = -670
x in (-oo:-670) U (-670:+oo)
(2*670*x)/(x+670) = 645 // - 645
(2*670*x)/(x+670)-645 = 0
(1340*x)/(x+670)-645 = 0
(1340*x)/(x+670)+(-645*(x+670))/(x+670) = 0
1340*x-645*(x+670) = 0
695*x-432150 = 0
(695*x-432150)/(x+670) = 0
(695*x-432150)/(x+670) = 0 // * x+670
695*x-432150 = 0
695*x-432150 = 0 // + 432150
695*x = 432150 // : 695
x = 432150/695
x = 86430/139
x = 86430/139
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