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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)
72/x+81/(x^2)+16 = 0
72*x^-1+81*x^-2+16 = 0
t_1 = x^-1
81*t_1^2+72*t_1^1+16 = 0
81*t_1^2+72*t_1+16 = 0
DELTA = 72^2-(4*16*81)
DELTA = 0
t_1 = -72/(2*81)
t_1 = -4/9 or t_1 = -4/9
t_1 = -4/9
x^-1+4/9 = 0
1*x^-1 = -4/9 // : 1
x^-1 = -4/9
-1 < 0
1/(x^1) = -4/9 // * x^1
1 = -4/9*x^1 // : -4/9
-9/4 = x^1
x = -9/4
t_1 = -4/9
x^-1+4/9 = 0
1*x^-1 = -4/9 // : 1
x^-1 = -4/9
-1 < 0
1/(x^1) = -4/9 // * x^1
1 = -4/9*x^1 // : -4/9
-9/4 = x^1
x = -9/4
x in { -9/4, -9/4 }
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