An error in Wikipedia? (trigonometry)

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It looks like they're the same.

The "arccosine" formula uses the ratio of the $i$th coordinate to the distance from the origin, whereas the "arccotangent" formula uses the ratio of the $i$th coordinate to the length of the projection of the radius onto the plane spanned by the other axes.

That is, notice that all the denominators are the same in the arccos formula, but not in the arccot formula.