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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
8/x+9 = (5/2)*x+15/4 // - (5/2)*x+15/4
8/x-((5/2)*x)-(15/4)+9 = 0
(-5/2)*x+8/x-15/4+9 = 0
8*x^-1-5/2*x^1+21/4*x^0 = 0
(21/4*x^1-5/2*x^2+8*x^0)/(x^1) = 0 // * x^2
x^1*(21/4*x^1-5/2*x^2+8*x^0) = 0
x^1
(-5/2)*x^2+(21/4)*x+8 = 0
(-5/2)*x^2+(21/4)*x+8 = 0
DELTA = (21/4)^2-(4*8*(-5/2))
DELTA = 1721/16
DELTA > 0
x = ((1721/16)^(1/2)-(21/4))/(2*(-5/2)) or x = (-(21/4)-(1721/16)^(1/2))/(2*(-5/2))
x = ((1721/16)^(1/2)-21/4)/(-5) or x = ((1721/16)^(1/2)+21/4)/5
x in { ((1721/16)^(1/2)-21/4)/(-5), ((1721/16)^(1/2)+21/4)/5}
x in { ((1721/16)^(1/2)-21/4)/(-5), ((1721/16)^(1/2)+21/4)/5 }
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