



 
Hi Lorne. The surface area of the main "openended" cone is the same as the surface area of a full (closed) cone minus the surface area of the cone that is a cap on the top. The surface area S of a cone is calculated based on the height h and the radius r at the base:
So we need to find these quantities first.
In similar triangles, the ratios of the side lengths is the same. This means that 10/7 = h/8. Thus, the h = 80/7 ft. If we use the formula for surface area above with r = 8 and h = 80/7, we can calculate the surface area of the full large (closed) cone. The surface area of the cap would come from using r = 1 and h = 80/7  10. Subtract these surface areas to complete the problem. Cheers,  


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