It appears that you assumed it was a circle and then drew the circle. But, I am not sure what else the problem would expect you to do to show it "geometrically". Plato showed an algebraic method of demonstration. I personally think his approach is a stronger demonstration, as it does not involve assuming the hypothesis first.
I had already worked out the problem algebraically but was curious as to how to answer geometrically as I wasn't taught it & have found only a few videos on answering this type of question. In terms of my answer I think it literally is that but what confuses me is the question itself tells me how to answer the question, so I'm thinking that can't be it?