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# FP1 (Edexcel) question on focus-directrix property watch

1. This is probably easy stuff for anyone here who's done FP1, but I'm having trouble getting my head round the basics:

Find the coordinates of the focus and an equation of the directrix of the parabola with equation: 4y=x^2 - 16

See I thought:
Standard form is x^2 = 4ay
For x^2 = 4y, a is (0,1) and directrix is y=-1
x^2 = 4(y + 4) is a vertical positive translation of x^2 = 4y by 4
so a is (0,5) and directrix is y=3

But no - plz help!
2. Actually solved it myself, i was transofrming wrong:

x^2 = 4(y + 4)
y+4=0.25x^2
y=0.25x^2 - 4

so downward translation of 4 from x^2 = 4y [y = 0.25x^2]
to give a is (0,-3), directrix is y + 5 = 0
3. That's FP3.
4. Off topic but it's scary how the grade 10/11 people in the US do this for Advanced Algebra.
I had to teach that and coming from an English educational background and not done the further maths modules before, I was like wt...o_O
5. Its the old FP2 actually. Does the new FP1 start next year?

To be honest, I'm not surprised its taught at grade 10/11. Limited as my knowledge of American education system is, I have an inclinged that they emphasis alot more on geometry than us brits do. So yeah I can definitely see this being taught. Its not difficult, just different really.

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