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

Look at the following set of numbers and determine if there is any property, if so, what is it?

\( 94,96,98,100,102,104 \)

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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