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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
8/7 = x-(4/x)-9 // - x-(4/x)-9
4/x-x+8/7+9 = 0
4*x^-1-1*x^1+71/7*x^0 = 0
(71/7*x^1-1*x^2+4*x^0)/(x^1) = 0 // * x^2
x^1*(71/7*x^1-1*x^2+4*x^0) = 0
x^1
(71/7)*x-x^2+4 = 0
(71/7)*x-x^2+4 = 0
DELTA = (71/7)^2-(-1*4*4)
DELTA = 5825/49
DELTA > 0
x = ((5825/49)^(1/2)-(71/7))/(-1*2) or x = (-(71/7)-(5825/49)^(1/2))/(-1*2)
x = ((5825/49)^(1/2)-71/7)/(-2) or x = ((5825/49)^(1/2)+71/7)/2
x in { ((5825/49)^(1/2)-71/7)/(-2), ((5825/49)^(1/2)+71/7)/2}
x in { ((5825/49)^(1/2)-71/7)/(-2), ((5825/49)^(1/2)+71/7)/2 }
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