Question

By attaching the edges of a circular sector of paper, a right circular cone is formed. What is the lateral surface area of the cone? The slant height is 8 units and the angle at the vertex is 40 degrees. Help, please~!~

Answer 1

assuming angle at the vertex means that, otherwise id need a better definition of 'angle at the vertex'.

it might mean the angle of the sector?


but then which part of the cone is used?

the lateral area of the cone is going to be the area of the sector that was used to create it .... the slant height would then relate to the radius of the circle that it was made from.

lets get a better idea of what this 'angle at the vertex' is describing.