Math Problem Statement

Consider this number pattern (8;5;2) Calculate the 15th term

Solution

The given number pattern is 8,5,28, 5, 2. To determine the 15th term, let's first identify the rule governing the pattern.

We can observe that each number is decreasing by 3:

  • 83=58 - 3 = 5
  • 53=25 - 3 = 2

This suggests that the pattern is an arithmetic sequence, where the common difference d=3d = -3.

The general formula for the nn-th term of an arithmetic sequence is:

an=a1+(n1)da_n = a_1 + (n - 1) \cdot d

Where:

  • ana_n is the nn-th term,
  • a1a_1 is the first term,
  • dd is the common difference,
  • nn is the position of the term in the sequence.

Given:

  • a1=8a_1 = 8,
  • d=3d = -3,
  • n=15n = 15.

Substitute these values into the formula:

a15=8+(151)(3)a_{15} = 8 + (15 - 1) \cdot (-3) a15=8+14(3)a_{15} = 8 + 14 \cdot (-3) a15=842a_{15} = 8 - 42 a15=34a_{15} = -34

Thus, the 15th term of the sequence is 34\boxed{-34}.

Would you like to go over the details of the calculation or explore similar sequences? Here are some related questions:

  1. How can you determine if a sequence is arithmetic?
  2. What would happen if the common difference was positive instead of negative?
  3. How do you calculate the sum of the first nn terms of an arithmetic sequence?
  4. Can this formula be used for other types of sequences, like geometric sequences?
  5. What is the 20th term of the sequence?

Tip: When identifying an arithmetic sequence, always check the differences between consecutive terms to ensure they are constant!

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Math Problem Analysis

Mathematical Concepts

Arithmetic Sequences
Common Difference
Algebra

Formulas

a_n = a_1 + (n - 1) * d

Theorems

Arithmetic Sequence Formula

Suitable Grade Level

Grades 6-8