Find the Algebraic Expression: Converting Point Patterns to nth Term Formula

Sequence Patterns with Point Arrangements

In the drawing, four main structures of the series.

Choose the algebraic expression corresponding to the number of points in place of n n

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Let's find the formula for this sequence.
00:09 Count how many circles are in each term.
00:54 Now, substitute the first term into the equation to see if it works.
01:00 Let's check if the formula applies to the second term.
01:08 This formula doesn't match the second term, so it's not correct.
01:14 Keep going! Use the same method to find the right formula.
01:21 Check if the first term fits this new formula.
01:31 Let's see if it also works with the second term.
01:38 Oops! This formula doesn't fit the second term.
01:48 Test the first term again with a different formula.
01:59 The first term doesn't match. Let's try another formula.
02:05 Test the first term with this formula.
02:12 Check it with the second term as well.
02:25 Great job! That's how we solve the problem.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

In the drawing, four main structures of the series.

Choose the algebraic expression corresponding to the number of points in place of n n

2

Step-by-step solution

The aim is to find a formula for the number of points (or dots) in structure based on the input n n . Let's consider the visible pattern in the structures:

By considering four instances, we deduce:

  • For n=0 n=0 : The structure has 2 points.
  • For n=1 n=1 : The structure has 4 points.
  • For n=2 n=2 : The structure has 6 points.
  • For n=3 n=3 : The structure has 8 points.

Observing closely, each subsequent structure increases by 2 points consistently.

Now, we try to formulate this pattern algebraically:

The number of points seems directly proportional to n n , leading to the formula 2(n+1) 2(n + 1) , where each increase in n n results in 2 additional points.

Verify:

  • For n=0 n=0 , 2(0+1)=2 2(0 + 1) = 2 .
  • For n=1 n=1 , 2(1+1)=4 2(1 + 1) = 4 .
  • For n=2 n=2 , 2(2+1)=6 2(2 + 1) = 6 .
  • For n=3 n=3 , 2(3+1)=8 2(3 + 1) = 8 .

The pattern and derived expression 2(n+1) 2(n + 1) consistently apply.

Thus, the answer is 2(n+1) \boxed{2(n + 1)} .

From the choices provided, the correct algebraic expression for the number of points in place of n n corresponds directly to choice 2: 2(n+1) 2(n + 1) .

3

Final Answer

2(n+1) 2(n+1)

Key Points to Remember

Essential concepts to master this topic
  • Pattern Recognition: Count points in each structure to identify the sequence
  • Formula Development: For n=0: 2 points, n=1: 4 points gives 2(n+1) 2(n+1)
  • Verification: Test formula with all given structures: 2(3+1)=8 2(3+1) = 8 points ✓

Common Mistakes

Avoid these frequent errors
  • Starting pattern count from n=1 instead of n=0
    Don't assume the first structure represents n=1 = wrong indexing! This shifts your entire pattern and gives formulas like 2(n+2) 2(n+2) instead. Always check if the pattern starts at n=0 by counting the actual structures shown.

Practice Quiz

Test your knowledge with interactive questions

Is there a term-to-term rule for the sequence below?

18 , 22 , 26 , 30

FAQ

Everything you need to know about this question

How do I know which structure represents n=0, n=1, etc.?

+

Look at the simplest structure first. The leftmost structure with 2 points represents n=0, then count sequentially: n=1 has 4 points, n=2 has 6 points, and so on.

What if I get a different formula that still works?

+

Multiple formulas can describe the same pattern! For example, 2n+2 2n + 2 equals 2(n+1) 2(n+1) . Always expand and simplify to check if your answer matches the given choices.

How do I spot the pattern when points are arranged differently?

+

Focus on counting total points in each structure, not their arrangement. Write down the sequence: 2, 4, 6, 8... then look for the common difference between consecutive terms.

Can I use trial and error with the answer choices?

+

Yes! Test each formula with the given structures. For n=0, n=1, n=2, n=3, check which formula gives 2, 4, 6, 8 points respectively. This is a great way to verify your pattern.

What does the '+1' represent in the formula 2(n+1)?

+

The '+1' accounts for the fact that we start counting at n=0 but still need 2 points minimum. It shifts the pattern so that when n=0, we get 2(0+1) = 2 points, not 0 points.

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