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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)
4/x+12/(x^2) = 5 // - 5
4/x+12/(x^2)-5 = 0
4*x^-1+12*x^-2-5 = 0
t_1 = x^-1
12*t_1^2+4*t_1^1-5 = 0
12*t_1^2+4*t_1-5 = 0
DELTA = 4^2-(-5*4*12)
DELTA = 256
DELTA > 0
t_1 = (256^(1/2)-4)/(2*12) or t_1 = (-256^(1/2)-4)/(2*12)
t_1 = 1/2 or t_1 = -5/6
t_1 = -5/6
x^-1+5/6 = 0
1*x^-1 = -5/6 // : 1
x^-1 = -5/6
-1 < 0
1/(x^1) = -5/6 // * x^1
1 = -5/6*x^1 // : -5/6
-6/5 = x^1
x = -6/5
t_1 = 1/2
x^-1-1/2 = 0
1*x^-1 = 1/2 // : 1
x^-1 = 1/2
-1 < 0
1/(x^1) = 1/2 // * x^1
1 = 1/2*x^1 // : 1/2
2 = x^1
x = 2
x in { -6/5, 2 }
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