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Exercise 949Algebra › Equations and radicalsL1Added 3 Nov 2026

A radical inequality

#radical inequality#squaring#cases

Statement

Solve in R\mathbb{R} the inequality
x+2≤x.\sqrt{x+2}\le x.

Hint

First determine the domain, then square (carefully: both sides must be nonnegative).

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Solution

Domain. x≥−2x\ge-2.

Case x<0x<0. x+2≥0>x\sqrt{x+2}\ge0>x, so no solution.

Case x≥0x\ge0. Both sides ≥0\ge0, so we can square: x+2≤x2x+2\le x^2, i.e. x2−x−2≥0x^2-x-2\ge0, i.e. (x−2)(x+1)≥0(x-2)(x+1)\ge0. On x≥0x\ge0, this gives x≥2x\ge2.

Conclusion. x≥2x\ge2.