Math Problem Statement

For the following geometric​ sequence, find a 9. 2​, two fifths ​, StartFraction 2 Over 25 EndFraction ​, StartFraction 2 Over 125 EndFraction ​, ... Question content area bottom Part 1 a 9equals    enter your response here ​(Type an integer or a simplified​ fraction.)

Solution

The given geometric sequence is:

2,25,225,2125,2, \frac{2}{5}, \frac{2}{25}, \frac{2}{125}, \dots

To find a9a_9, the 9th term of the sequence, we need to first identify the common ratio rr and then use the formula for the nn-th term of a geometric sequence:

an=a1rn1a_n = a_1 \cdot r^{n-1}

Step 1: Find the common ratio rr

The common ratio rr is found by dividing any term by the previous term. Let's divide the second term by the first term:

r=252=25×12=15r = \frac{\frac{2}{5}}{2} = \frac{2}{5} \times \frac{1}{2} = \frac{1}{5}

So, the common ratio r=15r = \frac{1}{5}.

Step 2: Use the formula for the nn-th term

Now, we can use the formula to find a9a_9:

a9=a1r91=2(15)8a_9 = a_1 \cdot r^{9-1} = 2 \cdot \left(\frac{1}{5}\right)^8

Step 3: Simplify the expression

a9=2158=21390625a_9 = 2 \cdot \frac{1}{5^8} = 2 \cdot \frac{1}{390625}

a9=2390625a_9 = \frac{2}{390625}

So, the 9th term a9=2390625a_9 = \frac{2}{390625}.

Let me know if you need further details or clarifications.

Related Questions:

  1. How do you find the common ratio of a geometric sequence?
  2. What happens to the terms of a geometric sequence as the common ratio gets smaller?
  3. How would you solve for the 10th term of this sequence?
  4. What is the sum of the first 9 terms of a geometric sequence?
  5. How do you check if a sequence is geometric?

Tip: When working with geometric sequences, the common ratio is key, and once you identify it, you can easily find any term using the formula an=a1rn1a_n = a_1 \cdot r^{n-1}.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences
Exponents
Fractions

Formulas

a_n = a_1 * r^(n-1)

Theorems

Geometric Sequence Formula

Suitable Grade Level

Grades 8-10