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Definition

Double Root of a Quadratic Equation

A double root (also called a repeated root) occurs when a quadratic equation has two identical solutions. When the left side of a quadratic equation can be written as the product of two identical factors — such as (y8)(y8)=0(y - 8)(y - 8) = 0 — applying the Zero Product Property produces the same equation twice, so only one distinct value of the variable satisfies the equation. That single repeated value is called a double root.

For example, if solving a quadratic equation leads to both y8=0y - 8 = 0 and y8=0y - 8 = 0, the solution y=8y = 8 appears twice. Rather than listing two separate solutions, the result is a single solution that counts with multiplicity two. Recognizing a double root is important because, unlike most quadratic equations that yield two different solutions, a squared-binomial equation equal to zero always yields exactly one solution.

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Updated 2026-04-21

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