Odpowiedź:
Szczegółowe wyjaśnienie:
1.
q = 2, S6 = 189
S6 = a1 *(1 - q^6)/(1 - q) = a1 *(1 - 64)/(1 - 2) = 63 a1
63 a1 = 189
a1 = 3
2.
7x-5, x+1, 1 - ciąg geometryczny tzn:
(x+1)² = (7x-5)*1
x²+2x + 1 - 7x + 5 = 0
x² - 5x + 6 = 0
Δ = 25 - 24 = 1
x1 = (5+1)/2 = 3
wtedy otrzymamy ciąg:
16, 4, 1
x2 = (5-1)/2 = 2
wtedy otrzymamy ciąg:
9, 3, 1
3.
a1 = -8 (chyba a1 ?)
a12 = 32 = a1 + 11*r
-8 + 11*r = 32
11*r = 40
r = 40/11
a15 = -8 + 14 * 40/11 = -8 + 560/11 = -88/11 + 560/11= 472/11 = 42 10/11
S15 = (a1 + a15)*15/2 = (-8 + 42 10/11)*15/2 = 15 * (34 10/11)/2
= 15*192/11 = 261 9/11
co to za głupie dane ! :(
