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Elemente de algebra liniara.pdf

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Spat¸ii vectoriale 25<br />

are o structură <strong>de</strong> spat¸iu vectorial real <strong>de</strong>finită prin<br />

<br />

x11<br />

x21<br />

x12<br />

x22<br />

x13<br />

x23<br />

<br />

y11<br />

+<br />

y21<br />

y12<br />

y22<br />

y13<br />

y23<br />

<br />

x11 + y11<br />

=<br />

x21 + y21<br />

x12 + y12<br />

x22 + y22<br />

x13 + y13<br />

x23 + y23<br />

<br />

<br />

x11<br />

α<br />

x21<br />

x12<br />

x22<br />

x13<br />

x23<br />

<br />

αx11<br />

=<br />

αx21<br />

αx12<br />

αx22<br />

αx13<br />

αx23<br />

<br />

.<br />

Exemplul 2.3 Mult¸imea F(R, C) a tuturor funct¸iilor ϕ : R −→ C are o structură<br />

<strong>de</strong> spat¸iu vectorial complex <strong>de</strong>finită <strong>de</strong><br />

(ϕ + ψ)(x) = ϕ(x) + ψ(x)<br />

(α ϕ)(x) = α ϕ(x), ∀α ∈ C.<br />

Exemplul 2.4 R are o structura <strong>de</strong> spat¸iu vectorial real în raport cu adunarea ¸si<br />

înmult¸irea uzuală.<br />

Exemplul 2.5 (C, +, ·), un<strong>de</strong><br />

este un spat¸iu vectorial real.<br />

(x1 + y1i) + (x2 + y2i) = x1 + x2 + (y1 + y2)i<br />

α(x + yi) = αx + αyi, ∀α ∈ R<br />

Exemplul 2.6 C are o structura <strong>de</strong> spat¸iu vectorial complex în raport cu adunarea<br />

¸si înmult¸irea numerelor complexe.<br />

2.2 Subspat¸ii vectoriale<br />

Definit¸ia 2.3 Fie V un spat¸iu vectorial peste K. Prin subspat¸iu vectorial al lui<br />

V se int¸elege orice submult¸ime W ⊆ V cu proprietatea<br />

x, y ∈ W<br />

α, β ∈ K<br />

<br />

=⇒ αx + βy ∈ W. (2.1)

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