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Sagot :
Answer:
[tex]\displaystyle S_{8}=6560[/tex]
Step-by-step explanation:
We have the geometric sequence:
2, 6, 18, 54 ...
And we want to find S8, or the sum of the first eight terms.
The sum of a geometric series is given by:
[tex]\displaystyle S=\frac{a(r^n-1)}{r-1}[/tex]
Where n is the number of terms, a is the first term, and r is the common ratio.
From our sequence, we can see that the first term a is 2.
The common ratio is 3 as each subsequent term is thrice the previous term.
And the number of terms n is 8.
Substitute:
[tex]\displaystyle S_8=\frac{2((3)^{8}-1)}{(3)-1}[/tex]
And evaluate. Hence:
[tex]\displaystyle S_8=6560[/tex]
The sum of the first eight terms is 6560.
Answer:
S₈ = 6560
Step-by-step explanation:
The sum to n terms of a geometric sequence is
[tex]S_{n}[/tex] = [tex]\frac{a(r^{n}-1) }{r-1}[/tex]
where a is the first term and r the common ratio
Here a = 2 and r = [tex]\frac{a_{2} }{a_{1} }[/tex] = [tex]\frac{6}{2}[/tex] = 3 , then
S₈ = [tex]\frac{2(3^{8}-1) }{3-1}[/tex]
= [tex]\frac{2(6561-1)}{2}[/tex]
= 6561 - 1
= 6560
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