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

Arithmetic Sequences with Negative Terms

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

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

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
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 written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

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

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

2

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 .

3

Final Answer

n5 n-5

Key Points to Remember

Essential concepts to master this topic
  • Pattern: Find the common difference between consecutive terms
  • Technique: Calculate 3(4)=1 -3 - (-4) = 1 for each pair
  • Check: Substitute n=1,2,3,4 into n5 n-5 gives -4,-3,-2,-1 ✓

Common Mistakes

Avoid these frequent errors
  • Confusing term-to-term rule with nth term formula
    Don't think 'add 1 to get next term' is the final answer = missing the algebraic formula! The question asks for the nth term rule, not just the pattern. Always express as n5 n-5 where n represents position number.

Practice Quiz

Test your knowledge with interactive questions

12 ☐ 10 ☐ 8 7 6 5 4 3 2 1

Which numbers are missing from the sequence so that the sequence has a term-to-term rule?

FAQ

Everything you need to know about this question

Why is the answer n-5 and not just 'add 1'?

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The question asks for the term-to-term rule as a formula. While 'add 1' describes the pattern, n5 n-5 is the algebraic rule that gives you any term directly based on its position.

How do I know if it's n-5 or something else?

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Test it! For position 1: 15=4 1-5 = -4 ✓. For position 2: 25=3 2-5 = -3 ✓. If your formula gives the correct sequence terms, you've found the right rule.

What if the sequence had different numbers?

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The same method works! Find the common difference, then use the pattern: first term + (position - 1) × common difference. For sequences starting at different values, the formula changes accordingly.

Why are we dealing with negative numbers?

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Negative numbers follow the same arithmetic sequence rules! The pattern -4, -3, -2, -1 still increases by 1 each time, just like positive sequences. Don't let the minus signs confuse the pattern.

Can I check my answer a different way?

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Yes! Pick any position number and see if your formula gives the correct term. Try position 3: 35=2 3-5 = -2 , which matches the third term in the sequence.

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