Parabola Help (1 Viewer)

[EkGew]

Consider the parabola y = x2 − 8x + 4. Find:

(i) the coordinates of the vertex,

(ii) the coordinates of the focus.

for (i) i think i found it to be (4,0) through completing the sqaure

(ii) but i cant exactly work out where the focus is. My guess it is still at the same place, but that doesnt make sense to me.

Thanks in advance

This is from the 2002 HSC paper.

/edit

Aso...what is the derivative of (1-t/60)....i just cant work it out...

 

[pLuvia]

(i)
y=x²-8x+4
y=(x-4)²-12
(x-4)²=(y+12)
Vertex: (4,-12)
(ii)Focus: (4,-11.75)
since 4a=1
a=1/4

d/dx(1-t/60)
=-1/60

Or do you mean

d/dx[(1-t)/60)
=-1/60

Either way, it's the same

 

[EkGew]

Thanks heaps. I see my stupidity there.
Cheers

And yeh i got that derivative....just wasnt 100% sure.