I am asked to prove that $\text{aff}(X)$ is closed in the topological sense. I found some posts where people show that it is closed under affine combinations (what it's quite obvious because the definition of affine set).
So i want to know if this prove is equivalent to show that $\text{aff}(X)$ is closed in the topological sense. In other case, I would like to know how to prove it.