Is there an easy way to just add a line to a plot by specifying the slope and intercept in the current diagram’s x/y coordinates?

I know one can do this by adding a scatter trace with line mode and either finding the min/max (x,y) points or just adding the ys for all the xs one has for the line, but in some cases all one has is the slope and intercept and doing this “manually” every time is just such a waste of time.