Arctan an arctangent function, which is a kind of inverse trigonometric function, that is, the inverse function of tangent function. Higher mathematics in general universities is involved.

For example: tan45 = 1, then arttan 1=45, this is the "inverse" operation, just like the "inverse" operation of multiplication is division.

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After introducing the concept of multivalued function, we can consider the inverse function (x∈R, and x≠kπ+π/2, k∈Z) of tangent function over its whole domain. At this time, the arctangent function is multivalued, denoted as y=Arctan x, and its domain is (-∞, +∞).

So y=arctan x (x∈(-∞, +∞), y∈(-π/2, π/2)) is called the principal value of the arctangent function, and y=arctan.