The Rule of 72 is a basic method to decide how stretched an investment
will take to double. It is specified with a fixed annual rate of interest. The
annual rate of return would be divided by 72, stockholders can now get an
approximate guess of how many years it will take for the original investment to
duplicate itself.
So basically, the formula is 72/r where r is the annual
rate. So the solution for this is to divide 72 by 18, to get the answer. The answer
is 4 years.
Since the focus is at (0, 2) and directrix is y = -2
point where both of these have the same x-value will be at (0, 2) for the focus and (0, -2) for the directrix.
The vertex will also have the same x-value so it will be (0, y).
y-value is half-way between the y-value of the focus, and the y-value of the directrix at x = 0.
Directrix y-value is -2 at x = 0 and for the focus it's 2 at x = 0.
Halfway between y = -2 and y = 2 is y = 0.
So the vertex of the parabola occurs at (0, 0).
So that's x^2 = 4ay = 4(2)y = 8y.
y = 1/8*x^2
hope it helps
Y-y1=m(x-x1)
y+18=1(x+8)
y=x-10
parallel lines have the same slope
