Question

Find the standard form of the equation of the parabola with a focus at (-4, 0) and a directrix at x = 4.

Answer 1

y^2 = 4ax
is a parabola where the focus is the point (a,0) and the directrix is x = -a

Answer 2

so you just have to plug in a = -4 into the above standard form

Answer 3

so you would get y^2=-16x?

Answer 4

right

Answer 5

and that is the answer? that isn't one of my choices
y2 = -8x

16y = x2

y = negative one divided by sixteenx2

x = negative one divided by sixteeny2

Answer 6

oh ok My memory might be failing me - I'll check it out

Answer 7

Thank you

Answer 8

check out this link
https://www.google.co.uk/search?q=y%5E2+%3D+4ax&espv=2&tbm=isch&tbo=u&source=univ&sa=X&ei=gzDEU_OYFaqw0AW0o4CYDA&sqi=2&ved=0CCYQsAQ&biw=1280&bih=595#facrc=_&imgdii=_&imgrc=jFMHP-6FeYodYM%253A%3BERSw5RaLEMmmsM%3Bhttp%253A%252F%252F3.bp.blogspot.com%252F-IjMRwQh6bVA%252FT_kQBdtjDdI%252FAAAAAAAABJs%252FudXIa-4swu8%252Fs320%252Fpara4.png%3Bhttp%253A%252F%252Fkelvinsonlinemaths.blogspot.com%252F2012%252F07%252Fparabola-as-locus.html%3B317%3B320

Answer 9

y^2 = -16x is correct

Answer 10

refer to the large square window to the right
if we replace a by 4 we get y^2 = -16x

and the directrix is at x = 4 (vertical line passing thru x=4)