We are given a geometric sequence $\{a_n\}$ such that $a_5 = 1$ and $a_8 = 8$. We are asked to find the common ratio $q$ of this geometric sequence.

AlgebraGeometric SequenceSequences and SeriesCommon Ratio
2025/4/18

1. Problem Description

We are given a geometric sequence {an}\{a_n\} such that a5=1a_5 = 1 and a8=8a_8 = 8. We are asked to find the common ratio qq of this geometric sequence.

2. Solution Steps

In a geometric sequence, the nn-th term can be written as an=a1qn1a_n = a_1 q^{n-1}, where a1a_1 is the first term and qq is the common ratio.
We are given a5=1a_5 = 1 and a8=8a_8 = 8.
So we have:
a5=a1q51=a1q4=1a_5 = a_1 q^{5-1} = a_1 q^4 = 1
a8=a1q81=a1q7=8a_8 = a_1 q^{8-1} = a_1 q^7 = 8
Dividing the second equation by the first equation, we get:
a1q7a1q4=81\frac{a_1 q^7}{a_1 q^4} = \frac{8}{1}
q3=8q^3 = 8
Taking the cube root of both sides, we get:
q=83=2q = \sqrt[3]{8} = 2

3. Final Answer

The common ratio q=2q = 2.

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