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Definition of annihilator

Annihilators:-

If V is a vector space over the field F and S is a subset of V,the annihilator of S is the set So of all linear functional f on V such that
f(α)=0   α∊S
Sometimes A(S) is also used to denote the annihilators of S.
Thus            S0={f∊V’: f(α)=0  α∊S}

Annihilator of an anhilator:-


Let V be a vector space over the field F.If S is any subset of V,then S0 is a subspace of V’.By definition of an annihilator, we have
(S0)0=S00={L∊V’: L(f)=0  ∀ f∊S0}
Obviously S00 is a subspace of V’’.But if V is finite dimensional then we have identified V’’ with V through the natural isomorphism αLα. Therefore we may regard S00 as a subspace of V.Thus

   S00={α∊V : f(α)=0  f∊S0}

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