how do i select inverse tan

anothaer name for inverse tangent is arctan (i think)

https://www.khanacademy.org/math/trigonometry/unit-circle-trig-func/inverse_trig_functions/v/inverse-trig-functions-arctan

arctangent or atan can be accessed by pressing 2nd and then atan

Thanks anon - that is exactly correct :)