if a cone is cut through the centre where it makes perpendicular to the vertex.what will be the surface area of the obtained half the cone

Answer 1

please any concept or formula for the previous question,i stuck

Answer 2

The curved part (and maybe the base) is just half the surface area of the cone, for which I'm sure you have the formula.

The interior which is exposed is just a triangle. Its area is also easy to find.