Square Root By Repeated Subtraction

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Created by: Team Maths - Examples.com, Last Updated: May 10, 2024

Square Root By Repeated Subtraction

The square root by repeated subtraction method is a foundational mathematical technique used to determine the square and square root of a number by sequentially subtracting consecutive odd integers. This approach not only introduces students to basic concepts in algebra and arithmetic but also links to more advanced topics such as rational and irrational numbers, emphasizing their practical applications in fields like statistics. By understanding how integers and their properties interact within this method, learners can better grasp concepts like the least squares method, which is pivotal in statistical analysis and data fitting. This method serves as an engaging gateway to exploring the broader implications of square and square roots across various mathematical disciplines.

What is Square Root by Repeated Subtraction?

Square Root by Repeated Subtraction is an elementary yet insightful method to find the square root of a perfect square number. This technique involves subtracting consecutive odd numbers from the number in question until the result reaches zero. The number of subtractions required to reach zero corresponds to the square root of the original number. This method provides a manual, intuitive approach to understanding square roots, especially beneficial for educational purposes in illustrating how squares and square roots function.


Let’s calculate the square root of 16 using this method:

  • Start with 16.
  • Subtract 1 (16 – 1 = 15)
  • Subtract 3 (15 – 3 = 12)
  • Subtract 5 (12 – 5 = 7)
  • Subtract 7 (7 – 7 = 0)

Finding Square Root Through Repeated Subtraction

The method of finding a square root through repeated subtraction is a straightforward yet educational technique used in mathematics, particularly beneficial for grasping the concept of square roots from a fundamental level. It involves subtracting consecutive odd numbers from the given number until the remainder is zero. This method is most effective with perfect square numbers and serves as a hands-on learning tool in understanding how numbers are composed.

Step 1: Start with Your Number

Identify the number from which you want to find the square root. Ensure that it is a perfect square to apply this method effectively.

Step 2: Subtract Consecutive Odd Numbers

Begin subtracting consecutive odd numbers starting from 1. After subtracting each odd number, subtract the next higher odd number from the result:

  • Subtract 1, then 3, then 5, and so on.

Step 3: Track the Number of Subtractions

Keep a count of how many times you subtract until the remainder equals zero. The process of subtraction should continue until no remainder is left.

Step 4: Result is the Square Root

The count of total subtractions you have made gives you the square root of the original number.

Example: Finding the Square Root of 49

  • Start with 49
  • Subtract 1 (49 – 1 = 48)
  • Subtract 3 (48 – 3 = 45)
  • Subtract 5 (45 – 5 = 40)
  • Subtract 7 (40 – 7 = 33)
  • Subtract 9 (33 – 9 = 24)
  • Subtract 11 (24 – 11 = 13)
  • Subtract 13 (13 – 13 = 0)

The number of subtractions was 7, which means the square root of 49 is 7.

Applications and Importance

This method is particularly useful in educational settings, helping students visualize and understand the process of finding square roots without the need for calculators. While it specifically applies to perfect squares, exploring this technique can also lead to discussions about rational and irrational numbers, algebraic principles, and integer properties. Moreover, the method fosters a foundational understanding that connects to more complex mathematical theories and statistical methodologies, such as the least squares method used in data fitting and prediction.

  • Applicability: It is only applicable to perfect squares. For numbers that are not perfect squares, this method cannot determine square roots precisely and does not address irrational roots.
  • Efficiency: For very large numbers, the process can become cumbersome and time-consuming compared to other methods like prime factorization or using a calculator.

Solved Problems – Finding Square Roots Through Repeated Subtraction

Example 1: Square Root of 25

Find the square root of 25 using the repeated subtraction method.

  • Start with 25.
  • Subtract 1 (25 – 1 = 24)
  • Subtract 3 (24 – 3 = 21)
  • Subtract 5 (21 – 5 = 16)
  • Subtract 7 (16 – 7 = 9)
  • Subtract 9 (9 – 9 = 0)

Number of subtractions: 5, which is the square root of 25.

Example 2: Square Root of 36

Calculate the square root of 36 using repeated subtraction.

  • Start with 36.
  • Subtract 1 (36 – 1 = 35)
  • Subtract 3 (35 – 3 = 32)
  • Subtract 5 (32 – 5 = 27)
  • Subtract 7 (27 – 7 = 20)
  • Subtract 9 (20 – 9 = 11)
  • Subtract 11 (11 – 11 = 0)

Number of subtractions: 6, which is the square root of 36.


How do you perform the square root by repeated subtraction?

To perform the square root by repeated subtraction, start with your target number and subtract consecutive odd numbers beginning with 1, then 3, 5, 7, and so on, until you reach zero. The total number of times you subtract is the square root of the original number.

Can the square root by repeated subtraction method be used for any number?

This method is only applicable to perfect squares. If the number is not a perfect square, the process will not end with a remainder of zero, and you will not get a whole number as a square root.

What are the limitations of the square root by repeated subtraction method?

The main limitation of this method is that it only works accurately for perfect squares. Additionally, it can be time-consuming and impractical for very large numbers. For non-perfect squares, the method will not yield a precise square root.

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