√ x^4 = √ 16 x^2 = 4 √ x^2 = ± √ 4 2,-2
or (x^2+4)(x^2-4) = 0 x^2 + 4 = 0 --> no real solution or x^2 - 4 = 0 (x+2)(x-2) = 0 x = ±2
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