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D( x )
x^4 = 0
x^4 = 0
x^4 = 0
1*x^4 = 0 // : 1
x^4 = 0
x = 0
x in (-oo:0) U (0:+oo)
x/2+1/(x^4) = 0
1/2*x+x^-4 = 0
x*(x^-5+1/2) = 0
1*x^-5 = -1/2 // : 1
x^-5 = -1/2
-5 < 0
1/(x^5) = -1/2 // * x^5
1 = -1/2*x^5 // : -1/2
-2 = x^5
x^5 = -2 // ^ 1/5
x = -2^(1/5)
x = 0
x = 0
x in { 0}
x = -2^(1/5)
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