Răspuns:
Explicație pas cu pas:
progresia geometrică:4 2 1 ....
a₂₈ = ?
S₁₀₃ = ?
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a₂ = a₁q => q = a₂/a₁ = 2/4 = 1/2
a₃ = a₂q => q = a₃/a₂ = 1/2
a₂₈ = a₁q²⁷ = 4·(1/2)²⁷ => a₂₈ = 1/2²⁵
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a₁₀₃ = a₁q¹⁰² = 4·(1/2)¹⁰² = 1/2¹⁰⁰
S₁₀₃ = 4+2+1 + 1/2 + 1/4 +.....+1/2¹⁰⁰ => S₁₀₃ = 7 + a
a = 1/2 + 1/4 +.....+1/2¹⁰⁰ I·2 =>
2a = 2/2 + 2/4 + ....+2/2¹⁰⁰ = 1+1/2+1/4+....+1/2⁹⁹
2a = 1+ a - 1/2¹⁰⁰ =>
a = 1 - 1/2¹⁰⁰
S₁₀₃ = 7 + 1 - 1/2¹⁰⁰ = > S₁₀₃ = 8 - 1/2¹⁰⁰
#copaceibrainly
