Display Equation from Graph

How do I display an equation from a graph in a note?

Here’s what I’m trying to do.
The equation f(x)=ax^2+bx+c is entered in a graph and a, b, c are defined.

How do I display the equation in a note, so it doesn’t show the – – or + – so that when I duplicate the screen and change the equation, the display automatically updates to the new equation?

I use this, but it gives the – – instead of + if I make b negative.

Any help would be greatly appreciated.