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D( x )
1-(4*x) = 0
1-(4*x) = 0
1-(4*x) = 0
1-4*x = 0
1-4*x = 0 // - 1
-4*x = -1 // : -4
x = -1/(-4)
x = 1/4
x in (-oo:1/4) U (1/4:+oo)
1/(1-(4*x)) = 1/5 // - 1/5
1/(1-(4*x))-(1/5) = 0
1/(1-4*x)-1/5 = 0
(1*5)/(5*(1-4*x))+(-1*(1-4*x))/(5*(1-4*x)) = 0
1*5-1*(1-4*x) = 0
4*x+4 = 0
(4*x+4)/(5*(1-4*x)) = 0
(4*x+4)/(5*(1-4*x)) = 0 // * 5*(1-4*x)
4*x+4 = 0
4*x+4 = 0 // - 4
4*x = -4 // : 4
x = -4/4
x = -1
x = -1
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