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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
25/x = 4/9 // - 4/9
25/x-(4/9) = 0
25/x-4/9 = 0
25*x^-1 = 4/9 // : 25
x^-1 = 4/225
-1 < 0
1/(x^1) = 4/225 // * x^1
1 = 4/225*x^1 // : 4/225
225/4 = x^1
x = 225/4
x = 225/4
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