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D( f )
f = 0
f = 0
f = 0
f in (-oo:0) U (0:+oo)
27/36 = 6/f // - 6/f
27/36-(6/f) = 0
27/36-6*f^-1 = 0
-6*f^-1 = -3/4 // : -6
f^-1 = 1/8
-1 < 0
1/(f^1) = 1/8 // * f^1
1 = 1/8*f^1 // : 1/8
8 = f^1
f = 8
f = 8
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