If a semi circle is rotated about the y axis as shown below, what three dimensional figure would be formed

The answer for the question shown above is: the  three dimensional figure that it would be formed is a sphere.  imagine that you rotate a semicircle in a plane about the y-axis , you will notice that resulting figure is a sphere. a sphere is define as a three-dimensional figure or a solid figure. many known objects has the form of a sphere, for example:   basketball balls, golf balls, planets  and others. 

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