Find the Element with 100 Squares in a Growing Geometric Pattern

The following is a sequence of structures formed from squares with side lengths of 1 cm.

In which element of the sequence are there 100 squares?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Will there be a term with 100 squares? If so, at which position?
00:05 Let's count the squares in each term
00:25 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
00:39 We want to find if there is a term with 100 squares
00:45 Let's substitute in the formula and solve for N
00:52 We'll take the square root to isolate N
00:57 N must be positive, there is no negative position in the sequence
01:00 And this is the solution to the question

Step-by-step written solution

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1

Understand the problem

The following is a sequence of structures formed from squares with side lengths of 1 cm.

In which element of the sequence are there 100 squares?

2

Step-by-step solution

To determine in which element in the sequence there are 100 squares, we need to identify the pattern of the sequence.

Let's denote n n as the position in the sequence and S(n) S(n) as the number of squares in the nth element.

Considering the structural pattern:

  • The first element (a single square): S(1)=1 S(1) = 1
  • The second element (form a 2x2 square = 4 squares): S(2)=4 S(2) = 4
  • The third element (form a 3x3 square = 9 squares): S(3)=9 S(3) = 9
  • The fourth element (form a 4x4 square = 16 squares): S(4)=16 S(4) = 16

From this, we observe that: S(n)=n2 S(n) = n^2 . This indicates that the number of squares in the nth element is n2 n^2 .

We want to find n n such that n2=100 n^2 = 100 .

Solving the equation n2=100 n^2 = 100 , we take the square root of both sides:

n=100=10 n = \sqrt{100} = 10

Therefore, the element in the sequence which contains 100 squares is the 10th element.

Thus, the solution to the problem is n=10 n = 10 .

3

Final Answer

10 10

Practice Quiz

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

18 , 22 , 26 , 30

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