Handwriting mathematical formalism
Office applications including PowerPoint, Excel and OneNote can create mathematical formalism by drawing with a tablet device.
In Excel, this is done from the Insert menu by selecting "Menu" and choosing the "Ink equation" option from the foot of the drop-down list. If you customise your ribbon, you can enable a "Draw" tab with a dedicated button. Word and PowerPoint have this "Draw" tab enabled by default.
You can convert ink to an equation after having drawn it. The Microsoft support page explains how.
Ink-to-maths functionality is not available natively in Google Sheets, but is included with paid add-ons such as MathType.