Question A.2: Finding a Polar Equation Find the polar equation of a parabo...

The eccentricity e must be 1, p must equal 3, and the equation must be of the following form.

r = \frac{ep}{1 – e \cos θ}

r = \frac{1 • 3}{1 – 1 \cos θ}     Substitute for e and p.

r = \frac{3}{1 – \cos θ}      Multiply.

The calculator graph in Figure 4 supports our result. When θ = 180°, r = 1.5. The distance from F(0, 0°)to the directrix is 2r = 2(1.5) = 3 units, as required.