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D( q )
q = 0
q = 0
q = 0
q in (-oo:0) U (0:+oo)
6.8 = 2/q // - 2/q
6.8-(2/q) = 0
6.8-2*q^-1 = 0
-2*q^-1 = -6.8 // : -2
q^-1 = 3.4
-1 < 0
1/(q^1) = 3.4 // * q^1
1 = 3.4*q^1 // : 3.4
0.29411765 = q^1
q = 0.29411765
q = 0.29411765
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