Given that the directrix is at y = 4 and the focus is at (0, -4), then the vertex is at (h, k) = (0, 0).
p is the distance between the vertex and the focus and between the vertex and the directrix = 4 and since the focus is below the directrix, p is negative, i.e. p = -4
Equation of a parabola is given by (x - h)^2 = 4p(y - k)
Therefore, the required equation is (x - 0)^2 = 4(-4)(y - 0)
x^2 = -16y
y = -1/16 x^2
Answer:
largest 4 digit number × largest 3 digit number
=9999 × 999
(10000-1)×(1000-1) = (a-b)(c-b)= ac-ab-bc+b^2
10000000-10000-1000+1 = 9989001
6 mm
Set up a proportion of 12/9=8/x. Cross multiply and this gives us 12x=72. Now divide both sides by 12 and you get 6.
