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D( x )
(x^2-4)^2 = 0
(x^2-4)^2 = 0
(x^2-4)^2 = 0
1*x^2 = 4 // : 1
x^2 = 4
x^2 = 4 // ^ 1/2
abs(x) = 2
x = 2 or x = -2
x in (-oo:-2) U (-2:2) U (2:+oo)
(20*x)/((x^2-4)^2) = 0
20*x = 0 // : 20
x = 0
x = 0
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