Math Problem Statement

The second term of a geometric sequence is 6 and the 5th term is 48 determine the sequence

Solution

To determine the geometric sequence, we need to find the first term (a1a_1) and the common ratio (rr) of the sequence. We know that:

  • The second term a2=6a_2 = 6
  • The fifth term a5=48a_5 = 48

The general formula for the nnth term of a geometric sequence is:

an=a1r(n1)a_n = a_1 \cdot r^{(n-1)}

Using this formula, we can express the second and fifth terms:

a2=a1r(21)=a1r=6a_2 = a_1 \cdot r^{(2-1)} = a_1 \cdot r = 6

a5=a1r(51)=a1r4=48a_5 = a_1 \cdot r^{(5-1)} = a_1 \cdot r^4 = 48

Now, divide the equation for the fifth term by the equation for the second term:

a5a2=a1r4a1r=r3=486=8\frac{a_5}{a_2} = \frac{a_1 \cdot r^4}{a_1 \cdot r} = r^3 = \frac{48}{6} = 8

Thus,

r3=8r=83=2r^3 = 8 \quad \Rightarrow \quad r = \sqrt[3]{8} = 2

Now that we have r=2r = 2, substitute this back into the equation for the second term to find a1a_1:

a12=6a1=62=3a_1 \cdot 2 = 6 \quad \Rightarrow \quad a_1 = \frac{6}{2} = 3

So, the first term is a1=3a_1 = 3 and the common ratio is r=2r = 2. Therefore, the sequence is:

3,6,12,24,48,3, 6, 12, 24, 48, \ldots

This is the geometric sequence.

Would you like more details or have any questions about this? Here are some related questions:

  1. What is the 10th term of this sequence?
  2. How would the sequence change if the common ratio were -2?
  3. What is the sum of the first 5 terms of this sequence?
  4. How do you find the nth term of a geometric sequence?
  5. What if the second term was given as 12 instead of 6?

Tip: The common ratio in a geometric sequence can be found by dividing any term by its previous term.

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Math Problem Analysis

Mathematical Concepts

Geometric Sequences

Formulas

Formula for the nth term of a geometric sequence: $a_n = a_1 \cdot r^{(n-1)}$

Theorems

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Suitable Grade Level

High School