MathematicsClass 8Squares and Square Roots

Finding Square Roots by Prime Factorization

Computing the square root of a number by breaking it down into its prime factors.

Class 8 · MathematicsCBSE & ICSE SOF IMO

Definition

Finding the square root using prime factorization is a method where a composite number is broken down into its prime factors. By grouping these prime factors into pairs of identical numbers, one factor from each pair is taken to find the square root. This method is most efficient for small or medium-sized numbers that can be easily factored.

Key formula

sqrt(a * a * b * b) = a * b

Worked examples

1

To find sqrt(784), find prime factors: 784 = 2 * 2 * 2 * 2 * 7 * 7. Grouping pairs gives (2 * 2 * 7), so the square root is 28.

2

To find sqrt(1764), prime factorization yields 2 * 2 * 3 * 3 * 7 * 7. Taking one from each pair gives 2 * 3 * 7 = 42.

3

To find sqrt(441), prime factorization yields 3 * 3 * 7 * 7. Taking one from each pair gives 3 * 7 = 21.

Common mistakes

  • Forgetting to group the prime factors into pairs before extracting them.
  • Using composite numbers instead of prime numbers during the factorization steps.
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