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D( y )
y = 0
y = 0
y = 0
y in (-oo:0) U (0:+oo)
4/y-5 = (5/2)*y // - (5/2)*y
4/y-((5/2)*y)-5 = 0
(-5/2)*y+4/y-5 = 0
4*y^-1-5/2*y^1-5*y^0 = 0
(4*y^0-5/2*y^2-5*y^1)/(y^1) = 0 // * y^2
y^1*(4*y^0-5/2*y^2-5*y^1) = 0
y^1
(-5/2)*y^2-5*y+4 = 0
(-5/2)*y^2-5*y+4 = 0
DELTA = (-5)^2-(4*4*(-5/2))
DELTA = 65
DELTA > 0
y = (65^(1/2)+5)/(2*(-5/2)) or y = (5-65^(1/2))/(2*(-5/2))
y = (65^(1/2)+5)/(-5) or y = (5-65^(1/2))/(-5)
y in { (65^(1/2)+5)/(-5), (5-65^(1/2))/(-5)}
y in { (65^(1/2)+5)/(-5), (5-65^(1/2))/(-5) }
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