What is the standard form of the equation of the parabola with a directrix at x=-5 and a focus at (-2,-5)?

Question

1404 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-01-21T11:35:36

The equation is #(y+5)^2=6(x+7/2)#

Any point #(x,y)# on the parabola is equidistant from the directrix and the focus.

Therefore,

#x+5=sqrt((x+2)^2+(y+5)^2)#

#(x+5)^2=(x+2)^2+(y+5)^2#

#x^2+10x+25=x^2+4x+4+(y+5)^2#

#(y+5)^2=6x+21#

#(y+5)^2=6(x+7/2)#

The vertex is #(-7/2,-5)#

graph{((y+5)^2-6(x+7/2))(y-100x-500)((x+2)^2+(y+5)^2-0.05)=0 [-28.86, 28.86, -20.2, 8.68]}