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mihai_michel
Pe: 2014-02-03T10:54:10+02:00 In: In:

progresie geometrica

Salu!Am urmatorul exercitiu pe care nu stiu sa-l fac sistem a_indice5-a_indice1=-1218 a_indice4-a_indice2=-420.I-am exprimat pe toti in functie a_1 si q ,dar nu mi-a iesit

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  1. wehrmacht

    salut !

        \[ \begin{array}{l} \left\{ \begin{array}{l} a_5 - a_1 = - 1218 \\ a_4 - a_2 = - 420 \\ \end{array} \right. \\ \Leftrightarrow \left\{ \begin{array}{l} a_1 \cdot q^4 - a_1 = - 1218 \\ a_1 \cdot q^3 - a_1 \cdot q = - 420 \\ \end{array} \right. \\ avem \\ \left\{ \begin{array}{l} a_1 \left( {q^4 - 1} \right) = - 1218 \\ a_1 q\left( {q^2 - 1} \right) = - 420 \\ \end{array} \right. \\ Le.impartim = > \\ \frac{{a_1 \overbrace {\left( {q^2 - 1} \right)\left( {q^2 + 1} \right)}^{q^4 - 1}}}{{a_1 q\left( {q^2 - 1} \right)}} = \frac{{ - 1218}}{{ - 420}} = > \frac{{q^2 + 1}}{q} = \frac{{203}}{{70}} = > 70q^2 + 70 - 203q = 0 \Leftrightarrow \\ 70q^2 - 203q + 70 = 0(ecuatia.de.gradul.II) = > ... \\ \end{array} \]

  2. mihai_michel

    Mersi mult!

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