If a point (x#,y#,z#) lies somewhere on a triangle (A,B,C), and the three triangle vertices all have different normals, how do you interpolate what the normal should be at the point in question?

Point=x,y,z

Triangle=

Ax,Ay,Az

Bx,By,Bz

Cx,Cy,Cz

Anx,Any,Anz

Bnx,Bny,Bnz

Cnx,Cny,Cnz

What should the normal be at the point (x,y,z)?

This is for a lightmapper. I need to figure out the normal at each point, so I can make the light appear smooth.