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D( x )
125-(0.3*x) = 0
125-(0.3*x) = 0
125-(0.3*x) = 0
125-0.3*x = 0
125-0.3*x = 0 // - 125
-0.3*x = -125 // : -0.3
x = -125/(-0.3)
x = 416.66666667
x in (-oo:416.66666667) U (416.66666667:+oo)
0.631 = (0.3*x)/(125-(0.3*x)) // - (0.3*x)/(125-(0.3*x))
0.631-((0.3*x)/(125-(0.3*x))) = 0
0.631-0.3*x*(125-0.3*x)^-1 = 0
(-0.3*x)/(125-0.3*x)+0.631 = 0
(-0.3*x)/(125-0.3*x)+(0.631*(125-0.3*x))/(125-0.3*x) = 0
0.631*(125-0.3*x)-0.3*x = 0
78.875-0.4893*x = 0
(78.875-0.4893*x)/(125-0.3*x) = 0
(78.875-0.4893*x)/(125-0.3*x) = 0 // * 125-0.3*x
78.875-0.4893*x = 0
78.875-0.4893*x = 0 // - 78.875
-0.4893*x = -78.875 // : -0.4893
x = -78.875/(-0.4893)
x = 161.199673
x = 161.199673
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