The {{KW|ATN}} or arctangent function returns the angle in radians of a numerical [[TAN|tangent]] value.


{{PageSyntax}}
:: radian_angle = '''ATN(''tangent!'')'''


{{PageDescription}}
* The [[SINGLE]] or [[DOUBLE]] ''tangent'' value would be equal to the tangent value of an angle. EX: [[TAN]](ATN(1)) = 1
* The return is that tangent value's ''angle'' in radians. To convert from radians to degrees, multiply radians * (180 / π).
* The function return value is between -π / 2 and π / 2.


''Example 1:'' When the [[TAN]]gent value equals 1, the line is drawn at a 45 degree angle(.7853982 radians) where [[SIN]] / [[COS]] = 1.
{{CodeStart}} '' ''
{{Cl|SCREEN}} 12
x = 100 * {{Cl|COS}}({{Cl|ATN}}(1))
y = 100 * {{Cl|SIN}}({{Cl|ATN}}(1))
{{Cl|LINE}} (200, 200)-(200 + x, 200 + y) '' ''
{{CodeEnd}}


''Example 2:'' {{KW|ATN}} can be used to define π in [[SINGLE]] or [[DOUBLE]] precision. The calculation can NOT be used as a [[CONST]]ant.
{{CodeStart}} '' ''
Pi = 4 * {{Cl|ATN}}(1)   '{{Cl|SINGLE}} precision
Pi# = 4 * {{Cl|ATN}}(1#) '{{Cl|DOUBLE}} precision
PRINT Pi, Pi# '' ''
{{CodeEnd}}


{{PageSeeAlso}}
* [[TAN]] {{text|(tangent)}}
* [[SIN]], [[COS]]
* [[Mathematical Operations]]
* [[Mathematical_Operations#Derived_Mathematical_Functions|Derived Mathematical Functions]]


{{PageNavigation}}