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Slika - Shrani.si

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A. Juriˇ<strong>si</strong>ć in V. Batagelj: Verjetnostni račun in statistika 235<br />

✬<br />

Če imata spremenljivki X in Y končni disperziji, jo ima tudi njuna vsota<br />

X + Y in velja<br />

✫<br />

D(X + Y ) = DX + DY + 2Cov(X, Y ).<br />

Če pa sta spremenljivki nekorelirani, je enostavno<br />

D(X + Y ) = DX + DY.<br />

Zvezo lahko posploˇ<strong>si</strong>mo na<br />

<br />

n<br />

n<br />

D = DXi + <br />

Cov(Xi, Xj)<br />

i=1<br />

Xi<br />

i=1<br />

i=j<br />

in za paroma nekorelirane spremenljivke<br />

<br />

n<br />

<br />

D =<br />

i=1<br />

Xi<br />

n<br />

DX.<br />

Univerza v Ljubljani ▲<br />

❙ ▲<br />

▲<br />

i=1<br />

● ❙ ▲<br />

▲<br />

☛ ✖<br />

▲<br />

✩<br />

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