



 
Hi Tinashe, The circumference of a circle is $\pi$ times the diameter so in your circle the circumference is $10 \times \pi.$ Thus the $216^o$ sector of this circle, shaded blue, is subtended by an arc of length \[\frac{216}{360} \times 10 \times \pi \mbox{ centimeters}\] If you roll up the blue sector in the diagram above to form a cone then the arc of length \[\frac{216}{360} \times 10 \times \pi \mbox{ centimeters}\] forms the circumference of the base circle of the cone. Use the formula for the circumference of a circle to find the radius, BC, of the base circle. Use the triangle ABC to determine the vertical angle. Penny  


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