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D( x )
x = 0
x^2 = 0
x = 0
x = 0
x^2 = 0
x^2 = 0
1*x^2 = 0 // : 1
x^2 = 0
x = 0
x in (-oo:0) U (0:+oo)
9/x+1/(x^2)+20 = 0
9*x^-1+x^-2+20 = 0
t_1 = x^-1
1*t_1^2+9*t_1^1+20 = 0
t_1^2+9*t_1+20 = 0
DELTA = 9^2-(1*4*20)
DELTA = 1
DELTA > 0
t_1 = (1^(1/2)-9)/(1*2) or t_1 = (-1^(1/2)-9)/(1*2)
t_1 = -4 or t_1 = -5
t_1 = -5
x^-1+5 = 0
1*x^-1 = -5 // : 1
x^-1 = -5
-1 < 0
1/(x^1) = -5 // * x^1
1 = -5*x^1 // : -5
-1/5 = x^1
x = -1/5
t_1 = -4
x^-1+4 = 0
1*x^-1 = -4 // : 1
x^-1 = -4
-1 < 0
1/(x^1) = -4 // * x^1
1 = -4*x^1 // : -4
-1/4 = x^1
x = -1/4
x in { -1/5, -1/4 }
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