y = -1/2x + 5 should be your equation because it is 5 ft above sea level and its eroding, or going down, 1 ft per 20 years. So every year, the sand dune erodes 1/20 ft more.
Hope this helps!
<u><em>Answer:</em></u>
y^2 = 28x
<em><u>Step-by-step explanation:</u></em>
Since the directrix is horizontal, use the equation of a parabola that opens left or right.
(y−k)^2 = 4p(x−h)
Find the vertex.
(0,0)
Find the distance from the focus to the vertex.
p = 7
Substitute in the known values for the variables into the equation
(y−k)^2 = 4p(x−h).
(y−0)^2 = 4(7)(x−0)
Simplify.
<em>y^2 = 28x</em>
Answer: x = 3 - sqrt 17 / 2 , x = 3 + sqrt 17 / 2
Step-by-step explanation:
2x^2 = 4 + 6x
divide both sides by 2
x^2 = 2 + 3x
move expression to the left
x^2 - 2 - 3x = 0
reorder the terms
x^2 - 3x - 2 = 0
use the quadratic formula
x = - (-3) +- sqrt (-3)^2 - 4 x (-2) / 2 x 1
calculate
x = 3 +- sqrt 17 / 2
answer
x = 3 - sqrt 17 / 2 , x = 3 + sqrt 17 / 2