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D( x )
0.3-x = 0
0.3-x = 0
0.3-x = 0
0.3-x = 0 // - 0.3
-x = -0.3 // * -1
x = 0.3
x in (-oo:0.3) U (0.3:+oo)
3.4 = (X/(0.3-x))*(0.4-x) // - (X/(0.3-x))*(0.4-x)
3.4-((X/(0.3-x))*(0.4-x)) = 0
(-1*X*(0.4-x))/(0.3-x)+3.4 = 0
(-1*X*(0.4-x))/(0.3-x)+(3.4*(0.3-x))/(0.3-x) = 0
3.4*(0.3-x)-1*X*(0.4-x) = 0
X*x-0.4*X-3.4*x+1.02 = 0
(X*x-0.4*X-3.4*x+1.02)/(0.3-x) = 0
(X*x-0.4*X-3.4*x+1.02)/(0.3-x) = 0 // * 0.3-x
X*x-0.4*X-3.4*x+1.02 = 0
1.02-0.4*X-3.4*x = 0 // - 1.02-0.4*X
-3.4*x = -(1.02-0.4*X) // : -3.4
x = (-(1.02-0.4*X))/(-3.4)
x = 0.29411765*(1.02-0.4*X)
x = 0.29411765*(1.02-0.4*X)
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