How to make all cells be displayed in TraditionalForm
The best solution is to open Preferences > Evaluation and set the Format type of new Output (and Input) cells to TraditionalForm. This is the setting that I use (certainly for Output).
See Tricks of the Trade 9(1) for more information, including on the very useful Notation` package.
As an alternative/followup to my comment, you could use the $PrePrint variable to ensure that your outputs are always in TraditionalForm. Once you assign a value to $PrePrint, it will be applied to all inputs before printing them.
Just make sure that in your notebook you Clear[$PrePrint] before evaluating any cells which you do not want in TraditionalForm.
Changing the default format for input and output cells was possible using the Preferences dialog through Mathematica 11.0.
Starting in Version 11.1, these values can only be changed from the Option Inspector by adjusting the CommonDefaultFormatTypes values.
So you can take the following steps in Version 11.1:
- Edit ▶ Preferences ▶ Advanced ▶ Open Option Inspector
- Cell Options ▶ New Cell Defaults ▶ CommonDefaultFormatTypes
- "Output" ▶ Change StandardForm to TraditionalForm
You can also refer to this document for more details:
How do I change the default format type of new cells?