Where are the 4th roots of 16i located?

If z is a fourth root of 16i, then z⁴ = 16i, so |z|⁴ = |16i| = 16. Thus |z| = 16^(1/4) = 2. All four roots lie on a circle centered at the origin with radius 2, so the correct choice is “on a circle with radius 2.”

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