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Tiếng ViệtCircles and PiSolids
In the previous sections, we studied the properties of circles on a flat surface. But our world is actually three-dimensional, so lets have a look at some 3D solids that are based on circles:
A A cylinder is a three-dimensional solid consisting of two congruent, parallel, circular sides (the bases), joined by a curved surface. You could also think of a cylinder as a “circular prism”.
A A cone is a three-dimensional solid that has a circular base joined to a single point (called the vertex) by a curved side. You could also think of a cone as a “circular pyramid”. A right cone is a cone with its vertex directly above the center of its base.
Every point on the surface of a A sphere is a three-dimensional solid consisting of all points that have the same distance from a given center. This distance is called the radius of the sphere.
Notice how the definition of a sphere is almost the same as the definition of a