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D( a )
a = 0
a = 0
a = 0
a in (-oo:0) U (0:+oo)
10.5/a = 3.5 // - 3.5
10.5/a-3.5 = 0
10.5*a^-1 = 3.5 // : 10.5
a^-1 = 0.33333333
-1 < 0
1/(a^1) = 0.33333333 // * a^1
1 = 0.33333333*a^1 // : 0.33333333
3.00000003 = a^1
a = 3.00000003
a = 3.00000003
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