Take mobile phone wps software as an example, the operation is as follows:

1. Open the framed document with your mobile phone.

2. Click the edit button in the upper left corner to enter the editing interface.

3. Click on the lower left corner to enter the interface of mobile phone ribbon, as shown in the figure.

4. Click the text box to add text.

5. Click the symbol, find the check mark in the mathematical symbol, and then click.

6. It can be finished at last.