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a fost răspuns

Calculeaza:a(10)=4;
a(12)=100;
a(13)=????; ( progresie geometrica )
Heeeeeelp:> O haide, nu stie nimeni!?!?!? :|

Răspuns :

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[tex]a_{10}=4=>b_1\cdot q^9=4[1]\\ a_{12}=100=>b_1\cdot q^{11}=100[2]\\ \ [2]:[1]=>q^2=100:4=>q^2=25=>q=\pm5\\ b_1\cdot q^{11}=100|\cdot q=>b_1\cdot q^{12}=100q=>a_{13}=100q=\pm500 [/tex]

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