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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
x^2-x^2+9*x+2*x-(15/x)-3+21 = 0
x^2-x^2+9*x+2*x-15*x^-1-3+21 = 0
11*x^1-15*x^-1+18*x^0 = 0
(11*x^2+18*x^1-15*x^0)/(x^1) = 0 // * x^2
x^1*(11*x^2+18*x^1-15*x^0) = 0
x^1
11*x^2+18*x-15 = 0
11*x^2+18*x-15 = 0
DELTA = 18^2-(-15*4*11)
DELTA = 984
DELTA > 0
x = (984^(1/2)-18)/(2*11) or x = (-984^(1/2)-18)/(2*11)
x = (2*246^(1/2)-18)/22 or x = (-2*246^(1/2)-18)/22
x in { (-2*246^(1/2)-18)/22, (2*246^(1/2)-18)/22}
x in { (-2*246^(1/2)-18)/22, (2*246^(1/2)-18)/22 }
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