How to divide one triangle in mesh?

Hello. I want to divide one triangle in mesh, for example in two little triangles. but I don’t want to touch other triangles. what is the best way to do that? do I need to describe a new Vertices and Triangle arrays for whole mesh ? or is there any function of mesh that may help?

You can’t just split a triangle into two. You would need to re-do the whole mesh becasue you have to add a new vertex.