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Spike4all
Pe: 2013-12-27T22:10:25+02:00 In: In:

Progresie

Buna tuturor!Am mai postat anterior aceste 2 exercitii ,insa tot nu le.am finalizat.Are cineva idee cum sa procedez?
1.Sa se determine termenul de rang n al progresiei geometrice:
a)-1,1/3,-1/9,..
b) 2,1,1/2,…
2.Sa se determine primii 2 termeni al progresiei geometrice bn daca
a) b9=768 si b11=3072

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  1. aurel5
    maestru (V)

    Spike4all wrote:
    1.Sa se determine termenul de rang n al progresiei geometrice:

    a)-1,1/3,-1/9,..

    b) 2,1,1/2,…

    2.Sa se determine primii 2 termeni al progresiei geometrice bn daca

    a) b9=768 si b11=3072

    \it{\bl\Large 1a) \frac{..}{..}\\\;\\ \\\;\\b_1 = -1, b_2 = \frac{1}{3}\\\;\\b_2 = b_1\cdot q \Longrightarrow q = \frac{b_2}{b_1} = \frac{\frac{1}{3}}{-1} = - \frac{1}{3}\\\;\\ \\\;\\b_n = b_1\cdot q^{n-1} = -1\cdot (- \frac{1}{3})^{n-1} = -1\cdot(-1\cdot\frac{1}{3})^{n-1} = -1\cdot(-1)^{n-1}(\frac{1}{3})^{n-1} = (-1)^n\cdot(\frac{1}{3})^{n-1} = (-1)^n\cdot(\frac{1}{3})^n\cdot(\frac{1}{3})^{-1} = (- \frac{1}{3})^n\cdot 3}

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