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 | | http://functions.wolfram.com/01.15.26.0005.01 | 
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 | | ArcTan[x, y] == Arg[x + I y] /; Element[x, Reals] && Element[y, Reals] | 
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 | | Cell[BoxData[RowBox[List[RowBox[List[RowBox[List["ArcTan", "[", RowBox[List["x", ",", "y"]], "]"]], "\[Equal]", RowBox[List["Arg", "[", RowBox[List["x", "+", RowBox[List["\[ImaginaryI]", " ", "y"]]]], "]"]]]], "/;", RowBox[List[RowBox[List["Element", "[", RowBox[List["x", ",", "Reals"]], "]"]], "\[And]", RowBox[List["Element", "[", RowBox[List["y", ",", "Reals"]], "]"]]]]]]]] | 
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   <math xmlns='http://www.w3.org/1998/Math/MathML' mathematica:form='TraditionalForm' xmlns:mathematica='http://www.wolfram.com/XML/'>  <semantics>  <mrow>  <mrow>  <mrow>  <msup>  <mi> tan </mi>  <mrow>  <mo> - </mo>  <mn> 1 </mn>  </mrow>  </msup>  <mo> ( </mo>  <mrow>  <mi> x </mi>  <mo> , </mo>  <mi> y </mi>  </mrow>  <mo> ) </mo>  </mrow>  <mo> ⩵ </mo>  <mrow>  <mi> arg </mi>  <mo> ⁡ </mo>  <mo> ( </mo>  <mrow>  <mi> x </mi>  <mo> + </mo>  <mrow>  <mi> ⅈ </mi>  <mo> ⁢ </mo>  <mi> y </mi>  </mrow>  </mrow>  <mo> ) </mo>  </mrow>  </mrow>  <mo> /; </mo>  <mrow>  <mrow>  <mi> x </mi>  <mo> ∈ </mo>  <semantics>  <mi> ℝ </mi>  <annotation encoding='Mathematica'> TagBox["\[DoubleStruckCapitalR]", Function[Reals]] </annotation>  </semantics>  </mrow>  <mo> ∧ </mo>  <mrow>  <mi> y </mi>  <mo> ∈ </mo>  <semantics>  <mi> ℝ </mi>  <annotation encoding='Mathematica'> TagBox["\[DoubleStruckCapitalR]", Function[Reals]] </annotation>  </semantics>  </mrow>  </mrow>  </mrow>  <annotation-xml encoding='MathML-Content'>  <apply>  <ci> Condition </ci>  <apply>  <eq />  <apply>  <arctan />  <ci> x </ci>  <ci> y </ci>  </apply>  <apply>  <arg />  <apply>  <plus />  <ci> x </ci>  <apply>  <times />  <imaginaryi />  <ci> y </ci>  </apply>  </apply>  </apply>  </apply>  <apply>  <and />  <apply>  <in />  <ci> x </ci>  <reals />  </apply>  <apply>  <in />  <ci> y </ci>  <reals />  </apply>  </apply>  </apply>  </annotation-xml>  </semantics>  </math> 
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 | | Cell[BoxData[RowBox[List[RowBox[List["HoldPattern", "[", RowBox[List["ArcTan", "[", RowBox[List["x_", ",", "y_"]], "]"]], "]"]], "\[RuleDelayed]", RowBox[List[RowBox[List["Arg", "[", RowBox[List["x", "+", RowBox[List["\[ImaginaryI]", " ", "y"]]]], "]"]], "/;", RowBox[List[RowBox[List["x", "\[Element]", "Reals"]], "&&", RowBox[List["y", "\[Element]", "Reals"]]]]]]]]]] | 
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 | | Date Added to functions.wolfram.com (modification date) | 
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