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D( i )
4*i+7 = 0
4*i+7 = 0
4*i+7 = 0
4*i+7 = 0 // - 7
4*i = -7 // : 4
i = -7/4
i in (-oo:-7/4) U (-7/4:+oo)
(8*i+14)/(4*i+7) = 0
8*i+14 = 0 // - 14
8*i = -14 // : 8
i = -14/8
i = -7/4
i in { -7/4}
i belongs to the empty set
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