inverse tan button

Click the " 2nd " button in the top left.

Click " atan ".

Click the " 2nd " button again.

Type the number that you want to get the inverse tangent of.

Close the parenthese, just because it's good to.

Click " = "

Or you can just type in " atan(  ".

If you hit the  ' 2nd' button the 'tan' key will become  'atan'    which is  tan^-1