Math Problem Statement

Consider the geometric sequence {3, -6, 12, -24, ... }.

What is the 8th term of the sequence ?

Solution

To find the 8th term of the geometric sequence, we need to use the formula for the nth term of a geometric sequence:

an=a1r(n1)a_n = a_1 \cdot 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 1: Identify the first term a1a_1 and common ratio rr

  • The first term a1=3a_1 = 3.
  • To find the common ratio rr, divide the second term by the first term:

r=63=2r = \frac{-6}{3} = -2

So, the common ratio is r=2r = -2.

Step 2: Use the formula to find the 8th term

We want to find a8a_8, so substitute a1=3a_1 = 3, r=2r = -2, and n=8n = 8 into the formula:

a8=3(2)(81)=3(2)7a_8 = 3 \cdot (-2)^{(8-1)} = 3 \cdot (-2)^7

Now calculate (2)7(-2)^7:

(2)7=128(-2)^7 = -128

So:

a8=3(128)=384a_8 = 3 \cdot (-128) = -384

Final Answer:

The 8th term of the sequence is 384\boxed{-384}.


Would you like any further explanation or have any questions on the solution?

Here are some related questions:

  1. What is the 5th term of this geometric sequence?
  2. How do you determine the common ratio of a geometric sequence?
  3. What is the sum of the first 8 terms of this geometric sequence?
  4. How do geometric sequences relate to exponential functions?
  5. Can you identify the general form of a geometric sequence given just the first few terms?

Tip: When calculating terms in a geometric sequence, remember that the common ratio rr is constant between consecutive terms, and the sequence grows (or decays) exponentially based on this ratio.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Geometric Sequences
Exponential Growth/Decay

Formulas

nth term of geometric sequence: a_n = a_1 * r^(n-1)

Theorems

Geometric Sequence Formula

Suitable Grade Level

Grades 7-9