Math Problem Statement

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

Solution

Given that the first term (a1a_1) of the geometric sequence is 1 and the tenth term (a10a_{10}) is 4, we are asked to find the seventeenth term (a17a_{17}).

Step 1: Write the formula for the nth term of a geometric sequence.

The nth term of a geometric sequence is given by:

an=a1×rn1a_n = a_1 \times r^{n-1}

Where:

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

Step 2: Set up equations using the given information.

From the problem:

  • a1=1a_1 = 1
  • a10=4a_{10} = 4

Using the formula for the nth term for a10a_{10}:

a10=a1×r9a_{10} = a_1 \times r^{9}

Substitute a10=4a_{10} = 4 and a1=1a_1 = 1:

4=1×r94 = 1 \times r^9

Thus,

r9=4r^9 = 4

Step 3: Solve for the common ratio rr.

To find rr, take the 9th root of both sides:

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

Step 4: Find the 17th term (a17a_{17}).

Now, use the formula for the nth term to find a17a_{17}:

a17=a1×r16a_{17} = a_1 \times r^{16}

Substituting a1=1a_1 = 1 and r=49r = \sqrt[9]{4}:

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

Simplifying further:

a17=4169a_{17} = 4^{\frac{16}{9}}

Now, let's calculate 41694^{\frac{16}{9}}.The seventeenth term of the geometric sequence is approximately 11.7611.76.

Would you like more details or have any questions?

Here are five related questions to deepen your understanding:

  1. How do you find the common ratio of a geometric sequence if two non-consecutive terms are given?
  2. What is the general formula for the sum of the first nn terms in a geometric sequence?
  3. How can you determine if a sequence is geometric given a list of terms?
  4. How does the growth rate of a geometric sequence compare to an arithmetic sequence?
  5. How would you solve for the nth term if the sequence included negative or fractional common ratios?

Tip: In geometric sequences, knowing just two non-consecutive terms allows you to find the common ratio, which can be applied to determine any other term in the sequence.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences

Formulas

nth term of a geometric sequence: \( a_n = a_1 \times r^{n-1} \)

Theorems

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Suitable Grade Level

Grades 9-12