how do i make tan negative 1 on the caculator

2 ways

 

1) click tan and hold it, the button will change to atan

 

2) click on the button labeled "2nd", the buttons will all change including the tan button

It depends on the calculator. A TI-84 plus ce is a good and there are ones these: https://www.mathway.com/Algebra

https://www.symbolab.com/