Solve for x
x\in (-\infty,-20]\cup [20,\infty)
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x^{2}\geq 400
Add 400 to both sides.
x^{2}\geq 20^{2}
Calculate the square root of 400 and get 20. Rewrite 400 as 20^{2}.
|x|\geq 20
Inequality holds for |x|\geq 20.
x\leq -20\text{; }x\geq 20
Rewrite |x|\geq 20 as x\leq -20\text{; }x\geq 20.
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