The vertex form of parabola is y = a(x-h)^2+c, where (h, k) are
the coordinates of the vertex. (1/a)/4 = 1/4a is focal distance from the vertex (h,k), and x = h
is the axis of of symmetry
The given parabola is y = x^2-8x+2. To
convert this to vertex form we have to complete the x^2-8x into a perfect square by adding 4^2
so that x^2-8x+4^2 = (x-4)^2.
Therefore we add and subtract
4^2:
y = (x^2-8x+4^2) - 4^2+2.
y =
1(x-8)^2 -18 is in the required form.
The coordinates of the vertex
= (8, -18)
The focal length = 1/4*1 = 1/4 . So the ocus is 1/4 units
above the vertex (8,-18).
The axis of symmetry is x= 8, a || line
to y axis.
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