Multiply the slant height times the radius times pi. The radius, the perpendicular height (from tip to center), and the slant height are related by the Pythagorean theorem. This refers to the height along the slanted side of the cone, not the height from the tip of the cone to the center of the circle. Write that answer off to one side, somewhere where it is labeled "base area" and easy to find. You can round, but keep at least 3 digits after the decimal point for now. Otherwise, use 3.14 or your calculator's pi button to finish the multiplication and get a decimal version for the area. If the instructions say anything like "exact value", it means that you write the Greek letter for pi and leave it. Write the radius somewhere off to the side, where it's labeled and easy to find, because you will need it several times in several different calculations.įind the area of the base circle by squaring the radius and multiplying by pi. If you have the slant height and perpendicular height, use the Pythagorean theorem. If you have the diameter, cut it in half to get the radius. Identify the radius of the cone's base circle. Use this example to help with your other cone problems. This video will walk you through the process of finding the surface area of a cone when you also have to derive the slant height. Math always seems hardest until someone shows you how to do the problem and then it all seems just so simple.
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