Math Problem Statement

insert -2 geometric means between 10 and -160

Solution

To insert two geometric means between 10 and -160, we need to determine three terms of a geometric sequence: the first term (a1a_1), the two geometric means (a2a_2 and a3a_3), and the fourth term (a4a_4).

Step-by-Step Solution:

  1. Identify the Known Terms:

    • a1=10a_1 = 10 (first term)
    • a4=160a_4 = -160 (fourth term)
  2. Set Up the General Formula for the Geometric Sequence: In a geometric sequence, each term is found by multiplying the previous term by a common ratio rr. The general term of a geometric sequence is given by: an=a1rn1a_n = a_1 \cdot r^{n-1}

    Therefore: a2=a1ra_2 = a_1 \cdot r a3=a1r2a_3 = a_1 \cdot r^2 a4=a1r3a_4 = a_1 \cdot r^3

  3. Apply the Known Values: Since a4=160a_4 = -160 and a1=10a_1 = 10, we have: 160=10r3-160 = 10 \cdot r^3

  4. Solve for the Common Ratio rr: r3=16010=16r^3 = \frac{-160}{10} = -16 r=163=2r = \sqrt[3]{-16} = -2

  5. Determine the Geometric Means a2a_2 and a3a_3: a2=a1r=10(2)=20a_2 = a_1 \cdot r = 10 \cdot (-2) = -20 a3=a1r2=10(2)2=104=40a_3 = a_1 \cdot r^2 = 10 \cdot (-2)^2 = 10 \cdot 4 = 40

Final Answer:

The two geometric means between 10 and -160 are -20 and 40.

Would you like more details or have any other questions? Here are some related questions you might find interesting:

  1. What happens if you need to insert more than two geometric means?
  2. How would you find the geometric means if the sequence included more terms?
  3. Can a geometric sequence have both positive and negative terms? What are the implications?
  4. What if the sequence started with a negative number? How would that affect the geometric means?
  5. How do geometric sequences differ from arithmetic sequences in terms of their properties?

Tip: When working with geometric sequences, always check the sign of the common ratio carefully, as it significantly affects the sequence's behavior.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences

Formulas

General term of a geometric sequence: $a_n = a_1 \cdot r^{n-1}$

Theorems

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Suitable Grade Level

Grades 10-12