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D( x )
0.00412-x = 0
0.00412-x = 0
0.00412-x = 0
0.00412-x = 0 // - 0.00412
-x = -0.00412 // * -1
x = 0.00412
x in (-oo:0.00412) U (0.00412:+oo)
0.3 = (2*x)/(0.00412-x) // - (2*x)/(0.00412-x)
0.3-((2*x)/(0.00412-x)) = 0
0.3-2*x*(0.00412-x)^-1 = 0
(-2*x)/(0.00412-x)+0.3 = 0
(-2*x)/(0.00412-x)+(0.3*(0.00412-x))/(0.00412-x) = 0
0.3*(0.00412-x)-2*x = 0
0.001236-2.3*x = 0
(0.001236-2.3*x)/(0.00412-x) = 0
(0.001236-2.3*x)/(0.00412-x) = 0 // * 0.00412-x
0.001236-2.3*x = 0
0.001236-2.3*x = 0 // - 0.001236
-2.3*x = -0.001236 // : -2.3
x = -0.001236/(-2.3)
x = 0.00053739
x = 0.00053739
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