Пошаговое объяснение:
1) b₁ = 1/15; q = 2; n = 4; Sₙ = (b₁ · ( qⁿ - 1)) : (q - 1)
S₄ = ( ( 1/15 · ( 2⁴ - 1)) : (2 - 1) = ( 1/15 · 15) : 1 = 1 ⇒ S₄ = 1
2) S₆ - ?; b₁ = 8; b₂ = 12; b₃ = 18 ⇒ q = b₂ : b₁; n = 6
q = 12: 8 = 1,5; Sₙ = ( b₁(qⁿ - 1)) : (q - 1)
S₆ = ( 8 · ( 1,5⁶ - 1)) : (1,5 - 1) = 8 ·(3,375 - 1) · (3,375 + 1) : 0,5 =
= 4,375 · 2,375 · 8 : 0,5 = 166,25
ответ: S₆ = 166,25
Пошаговое объяснение:
1) b₁ = 1/15; q = 2; n = 4; Sₙ = (b₁ · ( qⁿ - 1)) : (q - 1)
S₄ = ( ( 1/15 · ( 2⁴ - 1)) : (2 - 1) = ( 1/15 · 15) : 1 = 1 ⇒ S₄ = 1
2) S₆ - ?; b₁ = 8; b₂ = 12; b₃ = 18 ⇒ q = b₂ : b₁; n = 6
q = 12: 8 = 1,5; Sₙ = ( b₁(qⁿ - 1)) : (q - 1)
S₆ = ( 8 · ( 1,5⁶ - 1)) : (1,5 - 1) = 8 ·(3,375 - 1) · (3,375 + 1) : 0,5 =
= 4,375 · 2,375 · 8 : 0,5 = 166,25
ответ: S₆ = 166,25