Circular line from axis to axis on scatterplot

New community member here. Apologies if this is the wrong place for this, but I've been searching and cannot find what I need. I am hopeful one of you can help. I have a standard x y scatter diagram and I am trying to plot or draw a couple of circular lines in it. To be clearer, let's say my X and Y axis are 0-10 with major intervals of 1. I am looking to draw a circular line so that it intersects at 8,0 and 0,8, as if though i punched a pin though 0,0 and tied a string with a pencil on the other end to it and used it to draw a radius.

Thank you very much for any help! I look forward to digging deeper here and becoming a more advanced Excel user.

Mark