What is square root

Last updated: April 1, 2026

Quick Answer: A square root is a number that, when multiplied by itself, produces the original number. For example, 4 is the square root of 16 because 4 × 4 = 16. Square roots are fundamental mathematical operations used in algebra, geometry, and engineering.

Key Facts

Understanding Square Roots

A square root is a mathematical operation that reverses squaring. When you square a number, you multiply it by itself (for example, 5² = 25). A square root asks the opposite question: what number, when multiplied by itself, equals this value? The square root of 25 is 5 because 5 × 5 = 25.

Notation and Terminology

Square roots are denoted using the radical symbol (√). In the expression √25 = 5, the symbol √ is the radical sign, 25 is the radicand (the number under the radical), and 5 is the square root. Mathematicians sometimes write this as 25^(1/2) using exponential notation.

Perfect Squares and Irrational Numbers

Perfect squares are numbers whose square roots are whole numbers:

However, not all square roots are whole numbers. For example, √2 ≈ 1.414, √3 ≈ 1.732, and √5 ≈ 2.236. These are irrational numbers that cannot be expressed as simple fractions and have infinite non-repeating decimal representations.

Positive and Negative Square Roots

Technically, every positive number has two square roots: one positive and one negative. For instance, both 3 and -3, when squared, equal 9. The principal square root is the positive value, so √9 = 3. However, when solving equations, both roots may be relevant: x² = 9 means x = 3 or x = -3.

Applications in Mathematics and Science

Square roots appear throughout mathematics and practical applications. They're essential for solving quadratic equations, calculating distances in geometry, physics formulas, engineering calculations, and statistical analysis. The Pythagorean theorem (a² + b² = c²) frequently requires calculating square roots to find side lengths of triangles.

Related Questions

What is the difference between a square root and squaring?

Squaring multiplies a number by itself (5² = 25), while a square root finds which number multiplies by itself to equal a value (√25 = 5). They're inverse operations.

How do you calculate square roots?

For perfect squares, memorization is common. For other numbers, calculators provide decimal approximations. Methods like long division or Newton's method allow manual calculation of approximations.

Why is the square root of 2 irrational?

The square root of 2 cannot be expressed as a ratio of whole numbers. Its decimal representation (1.414...) never terminates or repeats, making it irrational by definition.

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Sources

  1. Wikipedia - Square Root CC-BY-SA-4.0
  2. Britannica - Square Root CC-BY-SA-4.0