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1.5: Нерівності трикутника та Коші-Шварца
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Але $n^2 = (n_{\parallel} + n_{perp} )^2 = n_{\parallel}^2 + 2n_{\parallel} \cdot n_{\perp} + n_{\perp} = n_{\parallel}^2 + n_{\perp}^2$ , і так як $n_{\parallel}$ це timeslike і $n_{\perp}$ spaclik...Але $n^2 = (n_{\parallel} + n_{perp} )^2 = n_{\parallel}^2 + 2n_{\parallel} \cdot n_{\perp} + n_{\perp} = n_{\parallel}^2 + n_{\perp}^2$ , і так як $n_{\parallel}$ це timeslike і $n_{\perp}$ spaclike, у нас є (в $+---$ $n_{\parallel}^2 > 0$ підписі) і $n_{\perp}^2 < 0$ .