Copy of Curved Surface Area of Cones - by Anthony Or

What is the curved surface area of the cone?[br]Press the red point in the figure.[br]See http://ggbtu.be/m161406 to find the curved surface area.
– Yogesh Chauhan, Stephen Jull, olivia.korum, Anthony OR 柯志明

Information: Copy of Curved Surface Area of Cones - by Anthony Or