$x+sqrt\{b^2-y^2\}=\; a\; ln\; frac\{b+sqrt\{b^2-y^2\}\}\{y\}.$

References

• George Salmon (1879). A Treatise on the Higher Plane Curves: Intended as a Sequel to A Treatise on Conic Sections. Published by Hodges, Foster, and Figgis. Page 290.