Focal Points

The focal point of a circle is its center, and is called the focus. But an ellipse has two focal points, called foci, represented by F, F in Fig. 148, and by B, B in Fig. 149.

A produced line is one which extends out beyond the marking point. Thus in Fig. 148 that part of the line K between F and G represents the produced portion of line K.

Fig. 149. Fig. 149.

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