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D( f )
f = 0
f = 0
f = 0
f in (-oo:0) U (0:+oo)
10.78/f = 6.68 // - 6.68
10.78/f-6.68 = 0
10.78*f^-1 = 6.68 // : 10.78
f^-1 = 0.61966605
-1 < 0
1/(f^1) = 0.61966605 // * f^1
1 = 0.61966605*f^1 // : 0.61966605
1.61377245 = f^1
f = 1.61377245
f = 1.61377245
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