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2
C 16π ft
2
D 20π ft
Answer
Choice D is the correct answer. The surface area of this cylinder is equal to , where r = 2 ft
andh = 3 ft. The surface area is
Cones
Let’s start with a diagram of a cone so that you can get some sense of where the formula for its surface
area comes from.
The cone has a circular base with area . It also has a “face” whose area is a bit difficult to interpret.
It’s actually a sector, or fraction of a circle, that depends on the circumference of the circle, 2πr, and the
slant height, l.
The surface area of a cone is given by the formula, , where r is the radius of the base and l is
the slant height.
Spheres
Recall that a sphere is the set of all points in space that are equidistant from a given point. That equal
distance is the radius of the circle. This makes things simpler, because everything about a sphere
depends on its radius. And so the formula for its surface area depends only on its radius.
The surface area of a sphere is given by the formula , where r is the radius of the sphere.
