How do i disable italics when writing a math equation?

Are you actually serious? Word has so many features i simply do not understand nor use, and this is not possible? That seems pretty ridiculous...

Yes, I'm serious.

It's a standard convention in mathematical publishing that all variables (except sometimes vectors) are italicized. Microsoft had no reason to suspect you would want your equations to use roman characters instead.

There is an option that can be misapplied to do what you ask. Although variables are italicized, function names such as "sin" and "cos" are not italicized. Word has a list of recognized functions, and you can add to that list. With the cursor in an equation, click the dialog launcher arrow in the bottom right corner of the Tools group on the Equation Tools tab. In the dialog that opens, click the Recognized Functions button. In the next dialog, type one letter that you expect to use as a variable and click the Add button; then add other variables in the same way.

I must add to this discussion: The convention is definitely notto italicize the Greek "nabla" (i.e. \nabla) when using it to denote the gradient of a spatially variable function.

It took me quite a long time today to realize that PowerPoint would automatically italicize each "nabla" in my presentation every time I closed it and opened it again.

For now I seem to have fixed the problem by highlighting each "nabla" and selecting Equation Tools > Normal Text. I'm not entirely convinced that they won't all italicize again at some point.

Upon further investigation, it is clear that my issue is a bug. I'm using PowerPoint 2016. Just a minute ago I submitted feedback with a screenshot in the app. I described it as follows:

"There is a bug: In the equation editor, when I insert a Greek "nabla" by typing "\nabla", it correctly inserts the symbol without being italicized. But then if I save the presentation, close it, and open it again, the "nabla" is italicized. The only way to stop this is to highlight the "nabla" and select Equation Tools > Normal Text. I also included the Greek "Delta" in the screenshot, which does not exhibit the same buggy behavior."

Yes, I'm serious.

It's a standard convention in mathematical publishing that all variables (except sometimes vectors) are italicized. Microsoft had no reason to suspect you would want your equations to use roman characters instead.

There is an option that can be misapplied to do what you ask. Although variables are italicized, function names such as "sin" and "cos" are not italicized. Word has a list of recognized functions, and you can add to that list. With the cursor in an equation, click the dialog launcher arrow in the bottom right corner of the Tools group on the Equation Tools tab. In the dialog that opens, click the Recognized Functions button. In the next dialog, type one letter that you expect to use as a variable and click the Add button; then add other variables in the same way.

You can't turn it off completely. What you can do is type the equation, then select the whole equation and click the Normal Text button at the left end of the Equation Tools tab of the ribbon.