



 
Hi Elwin, Look at the first two diagrams in my response to a question from Steve a few years ago. You have the length $a$ of the arc to be 6 cm. When the sector is rolled up to form a cone this arc is the circumference of the circular base. The circumference of a circle is $\pi \times d$ where $d$ is the diameter. What is the diameter when the circumference is 6 cm? Harley  


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