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Negative Square Root Notation

Every positive number has two square roots — one positive and one negative — but the radical sign x\sqrt{\phantom{x}} by convention denotes only the positive (principal) square root. To indicate the negative square root, place a negative sign directly in front of the radical. For example, 100=10\sqrt{100} = 10 gives the positive square root, while 100=10-\sqrt{100} = -10 gives the negative square root. The expression 100-\sqrt{100} is read as "the opposite of the square root of 100100." This notation works because the negative sign acts on the already-evaluated radical: first compute the principal square root, then take its opposite.

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Updated 2026-04-21

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