<em><u>A solid of revolution is a three-dimensional figure obtained by rotating a two-dimensional figure (or curve) around a straight line (called the axis) that lies in the same plane. ... Since the triangle's interior is shaded, it creates the interior of the cone, creating a solid figure.</u></em>
<em><u>Three dimensional shapes are obtained by rotating the two dimensional shapes. When a circle is rotated we get sphere; when a triangle is rotated we get cone; when rectangle or square is rotated we get cylinder</u></em>
