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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
39 = 9.8/x // - 9.8/x
39-(9.8/x) = 0
39-9.8*x^-1 = 0
-9.8*x^-1 = -39 // : -9.8
x^-1 = 3.97959184
-1 < 0
1/(x^1) = 3.97959184 // * x^1
1 = 3.97959184*x^1 // : 3.97959184
0.25128205 = x^1
x = 0.25128205
x = 0.25128205
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