Math Problem Statement

What is the 10th term of the geometric sequence −4.5,−13.5,−40.5,−121.5,...

 ?   Enter the exact answer.   The 10th term is 

Solution

To find the 10th term of a geometric sequence, we use the formula:

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

Where:

  • ana_n is the nn-th term.
  • a1a_1 is the first term.
  • rr is the common ratio.
  • nn is the term number.

Step 1: Determine a1a_1 and rr

The first term (a1a_1) is 4.5-4.5.
The common ratio (rr) is calculated as:

r=a2a1=13.54.5=3r = \frac{a_2}{a_1} = \frac{-13.5}{-4.5} = 3

Step 2: Substitute into the formula

We want the 10th term (a10a_{10}):

a10=a1r101=4.539a_{10} = a_1 \cdot r^{10-1} = -4.5 \cdot 3^{9}

Step 3: Calculate 393^9

39=196833^9 = 19683

Substitute this back:

a10=4.519683=88573.5a_{10} = -4.5 \cdot 19683 = -88573.5

Final Answer:

The 10th term is:

88573.5\boxed{-88573.5}

Would you like further clarification or a breakdown of the calculations? 😊


Related Questions:

  1. How is the common ratio calculated in geometric sequences?
  2. What are the key differences between geometric and arithmetic sequences?
  3. How can we derive the sum of the first nn terms in a geometric sequence?
  4. Can geometric sequences include positive and negative terms?
  5. How do we solve for nn if a specific term value is given?

Tip:

When working with large exponents, breaking the computation into smaller steps can reduce errors!

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Math Problem Analysis

Mathematical Concepts

Sequences
Geometric Sequences
Exponential Growth

Formulas

an = a1 * r^(n-1)

Theorems

Properties of geometric sequences

Suitable Grade Level

Grades 8-10