Hi. This question is from the book Geometry by Brannam, Esplen, Gray and it comes from the chapter 7, section 1 review problems which cover introduction to spherical geometry. Determine the equation of the great circle that passes through the point (1 / sqrt(6), -1 / sqrt(6), 2 / sqrt(6)) This is probably a dumb question but I'm not even sure what the general equation for a circle in R^3 looks like, if I knew that then I think I could answer the question. I'm thinking (...without much justification...) that perhaps the equation of the circle in R^3 is like that of a plane in R^3? Where the coefficients of the x, y and z variables in the standard form, are the components of the normal vector ..? In other words I think I need to incorporate the normal to uniquely identify the specific circle of radius 1 which is centered at the origin because there are so many, but I'm not really sure how to do that and haven't had much success so far, and am a bit frustrated now :grumpy: Thanks.