Square Pattern Analysis: Finding the 81-Square Structure in a Sequence

Question

The following is a series of structures formed by squares with side lengths of 1 cm.

Is it possible to have a structure in the series that has 81 squares? If so, what element of the series is it?

Video Solution

Solution Steps

00:00 Will there be a term with 81 squares? If so, at which position?
00:04 Let's count the squares in each term
00:23 We can see that the number of squares equals the term's position squared
00:34 Therefore we can conclude this is the sequence formula
00:40 We want to find if there's a term with 81 squares
00:43 We'll substitute in the formula and solve for N
00:47 We'll take the square root to isolate N
00:50 When taking a square root there are always 2 solutions (positive and negative)
00:53 In a sequence there can't be a negative position, so the positive solution is correct
00:57 And this is the solution to the question

Step-by-Step Solution

To solve this problem, we take the following steps:

  • Step 1: Identify the series pattern.
    The provided structures correspond to perfect squares: 1, 4, 9, 16, etc.
  • Step 2: Determine if 81 is in this series.
    Since the number of squares follows n2 n^2 , we calculate whether 81 is a perfect square:
    n2=81 n^2 = 81 implies n=81 n = \sqrt{81} .
  • Step 3: Calculate the square root.
    Calculating 81 \sqrt{81} yields n=9 n = 9 .
  • Step 4: Verify the solution.
    Since 9 is a natural number and 92=81 9^2 = 81 , the ninth structure in the series has 81 squares.

Therefore, it is possible to have a structure in the series with 81 squares, and it is the ninth element of the series, explicitly identified by computing the sequence.

Based on the choices provided, the correct answer is: Yes, 9 9 .

Answer

Yes, 9 9