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Example

Simplifying 81c2-\sqrt{81c^2}

Simplify a square root that contains both a numerical perfect square and a variable squared, with a negative sign placed in front of the radical.

81c2-\sqrt{81c^2}

First, identify the expression whose square equals the radicand. Since (9c)2=81c2(9c)^2 = 81c^2, the principal square root is 81c2=9c\sqrt{81c^2} = 9c. Then apply the negative sign that sits in front of the radical:

81c2=9c-\sqrt{81c^2} = -9c

This example combines two previously learned skills: simplifying square roots of variable expressions (take the square root of the coefficient and halve the variable's exponent) and applying a negative sign in front of the radical (evaluate the square root first, then negate). The negative sign is not part of the radicand — it is applied after the square root has been computed.

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Updated 2026-04-21

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