DEF Definitions of Conics

Wang Muran
Any conic section can be defined as the locus of points whose distances to a point (the focus) and a line (the directrix) are in a constant ratio (the eccentricity). In this activity, we shall explore how eccentricity affects the shape of the conics.


1. Drag to set the fixed point F; drag the red dot to set the fixed line d. 2. Use the slider to adjust the eccentricity e. 3. Click the checkbox to construct the locus of the variable point P satisfying PF/Pd = e. 4. Click the 'Erase' button before constructing a new locus.


1. How does the eccentricity e affect the locus of P? 2. Predict the locus when e = 0.