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Definition

Extraneous Solution to a Radical Equation

An extraneous solution to a radical equation is a value that emerges from the algebraic solving process — typically from squaring both sides — but does not satisfy the original equation. Because the radical sign a\sqrt{a} denotes the principal (non-negative) square root, a0\sqrt{a} \geq 0 always holds. When both sides of a radical equation are squared, the resulting equation may have solutions that would force the square root expression to equal a negative number, which is impossible. Such a value is algebraically valid for the squared equation but invalid for the original radical equation and must be discarded. This parallels the concept of extraneous solutions in rational equations, where a solution may make a denominator zero; here, the issue is that a solution may require a principal square root to be negative.

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Updated 2026-04-21

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