Determine the Increment Pattern: From -4 to -1 in the Sequence

Question

What is the term-to-term rule for the sequence below?

4,3,2,1 -4,-3,-2,-1

Video Solution

Solution Steps

00:00 Find the sequence formula
00:03 Identify the first term according to the given data
00:07 Notice the constant difference between terms
00:20 This is the constant difference
00:26 Use the formula to describe an arithmetic sequence
00:33 Substitute appropriate values and solve to find the sequence formula
00:43 Properly expand brackets, multiply by each factor
00:53 Continue solving
01:03 And this is the solution to the question

Step-by-Step Solution

To solve this sequence problem, we will use the following steps:

  • Step 1: Identify the difference between the successive terms.
  • Step 2: Use the common difference to find the term-to-term rule.
  • Step 3: Verify the rule with the provided terms.

Let's go through each step:
Step 1: The sequence given is 4,3,2,1-4, -3, -2, -1. The difference between each successive pair of terms is +1+1 (e.g., 3(4)=1-3 - (-4) = 1, 2(3)=1-2 - (-3) = 1).
Step 2: Since the common difference dd is 11, this indicates the sequence is arithmetic and increases by 1 for each subsequent term. To form the term-to-term rule, we note that each term is calculated by adding 1 to the previous term.
Step 3: To express this rule in formula terms, consider nn as the number of the term, where n=1n = 1 corresponds to the first term. The first term is 4-4. By analyzing the sequence further, a formula aligning with these steps is an=n5a_n = n - 5 for the given terms (-4, -3, -2, -1). Substituting into this formula, for n=1,2,3,4n=1, 2, 3, 4, we obtain 4,3,2,1-4, -3, -2, -1 respectively.

Therefore, the term-to-term rule for the given sequence is n5 n-5 .

Answer

n5 n-5