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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
(4*x-5)/5 = 4/x // - 4/x
(4*x-5)/5-(4/x) = 0
(4*x-5)/5-4*x^-1 = 0
(4*x-5)/5-4/x = 0
(x*(4*x-5))/(5*x)+(-4*5)/(5*x) = 0
x*(4*x-5)-4*5 = 0
4*x^2-5*x-20 = 0
4*x^2-5*x-20 = 0
4*x^2-5*x-20 = 0
DELTA = (-5)^2-(-20*4*4)
DELTA = 345
DELTA > 0
x = (345^(1/2)+5)/(2*4) or x = (5-345^(1/2))/(2*4)
x = (345^(1/2)+5)/8 or x = (5-345^(1/2))/8
(x-((5-345^(1/2))/8))*(x-((345^(1/2)+5)/8)) = 0
((x-((5-345^(1/2))/8))*(x-((345^(1/2)+5)/8)))/(5*x) = 0
((x-((5-345^(1/2))/8))*(x-((345^(1/2)+5)/8)))/(5*x) = 0 // * 5*x
(x-((5-345^(1/2))/8))*(x-((345^(1/2)+5)/8)) = 0
( x-((345^(1/2)+5)/8) )
x-((345^(1/2)+5)/8) = 0 // + (345^(1/2)+5)/8
x = (345^(1/2)+5)/8
( x-((5-345^(1/2))/8) )
x-((5-345^(1/2))/8) = 0 // + (5-345^(1/2))/8
x = (5-345^(1/2))/8
x in { (345^(1/2)+5)/8, (5-345^(1/2))/8 }
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