Math Problem Statement

if the first and and tenth terms of a geometric sequence are 1 and 4, find the seventeenth term

Solution

To solve for the seventeenth term of the geometric sequence, let's start by recalling the formula for the nnth term of a geometric sequence:

an=a1r(n1)a_n = a_1 \cdot r^{(n-1)}

where:

  • ana_n is the nnth term,
  • a1a_1 is the first term,
  • rr is the common ratio,
  • nn is the term number.

Step 1: Identify the known values

Given:

  • The first term, a1=1a_1 = 1,
  • The tenth term, a10=4a_{10} = 4.

Step 2: Find the common ratio rr

The formula for the tenth term is:

a10=a1r9a_{10} = a_1 \cdot r^{9}

Substituting the known values:

4=1r94 = 1 \cdot r^9

r9=4r^9 = 4

Taking the ninth root of both sides to solve for rr:

r=49r = \sqrt[9]{4}

Step 3: Find the seventeenth term

Now, using the formula for the nnth term, we want to find the seventeenth term, a17a_{17}:

a17=a1r16a_{17} = a_1 \cdot r^{16}

Substituting the known values:

a17=1(49)16a_{17} = 1 \cdot \left(\sqrt[9]{4}\right)^{16}

Simplifying:

a17=(4169)a_{17} = \left(4^{\frac{16}{9}}\right)

Final Answer:

The seventeenth term is:

a17=416912.73a_{17} = 4^{\frac{16}{9}} \approx 12.73

This is the value of the seventeenth term.

Would you like more details or have any questions?


Here are 5 related questions to explore further:

  1. How do you find the sum of the first 17 terms of this geometric sequence?
  2. What would be the common ratio if the first term was 2 instead of 1, keeping the tenth term as 4?
  3. How does the geometric sequence change if the first term is negative?
  4. What is the general formula for the sum of an infinite geometric series?
  5. How would you solve for the 17th term if you were given a different geometric sequence?

Tip: Always remember that in geometric sequences, the common ratio rr determines how quickly the terms grow or shrink.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences

Formulas

Formula for nth term of a geometric sequence

Theorems

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Suitable Grade Level

Grades 9-12