Store quadratic formula MS access and retrieve it in datagridview

Storing it is pretty simple: I assume you have it a a rich text document in your RichTextBox and that you want to "keep the formatting"? If so, then that part is simple: get the RTF data from the RichRextBox using the Rtf property:

string rtf = myRichTextBox.Rtf;

Once it's in a string, you can store it a database like any other string based data.
Displaying RTF data in a DataGridView is harder though, but not impossible: RichTextBox Cell in a DataGridView[^] should help.