Math Problem Statement

Diketahui barisan geometri dengan suku ke-2 = -6 dan suku ke-5 = 48. Berapakah rasio pada barisan tersebut?

Solution

The problem is asking to find the common ratio (rr) of a geometric sequence where the second term (a2a_2) is 6-6 and the fifth term (a5a_5) is 4848.

In a geometric sequence, the nn-th term is given by 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, and
  • nn is the position of the term.

We are given:

  • a2=6a_2 = -6,
  • a5=48a_5 = 48.

We can set up two equations:

  1. a2=a1r1=6a_2 = a_1 \cdot r^1 = -6,
  2. a5=a1r4=48a_5 = a_1 \cdot r^4 = 48.

Step 1: Solve for a1a_1 and rr

From the first equation, a1r=6a_1 \cdot r = -6, so: a1=6ra_1 = \frac{-6}{r}

Substitute this into the second equation: (6r)r4=48\left(\frac{-6}{r}\right) \cdot r^4 = 48 Simplify: 6r3=48-6 \cdot r^3 = 48 r3=486=8r^3 = \frac{48}{-6} = -8

Step 2: Solve for rr

r=83=2r = \sqrt[3]{-8} = -2

Thus, the common ratio of the geometric sequence is r=2r = -2.

Would you like more details on any step? Here are some related questions:

  1. How do you derive the formula for the nth term of a geometric sequence?
  2. What are the conditions for a geometric sequence to be convergent or divergent?
  3. How would the process change if we had different terms given?
  4. Can you explain why a negative ratio causes alternating terms?
  5. How does the formula for geometric sequences apply to infinite series?

Tip: Always verify your result by substituting back into the original equations to ensure accuracy.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences
Algebra

Formulas

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

Theorems

Geometric sequence formula

Suitable Grade Level

Grades 10-12