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Arctangent
(trigonometry) Any of several single-valued or multivalued functions that are inverses of the tangent function. Symbol: arctan, tan^(-1) [Wiktionary]
Arctangent
Trigonometric functions - Vector stencils library
Cosine
Sine
Tangent
Cartesian coordinate system
Cartesian coordinate system in two dimensions
Arcsine
Arccosine
Arctangent