An equation of the parabola whose focus is (–3, 0)and the directrix x + 5 = 0 is:
y2=4(x+5)
y2=4(x+4)
y2=4(x+3)
y2=4(x−3)
We have (x+3)2+y2=|x+5|
⇒y2=(x+5)2−(x+3)2=4(x+4).