Question

An engineer is designing an arch-shaped gate for the entrance to an amusement park. The gate must be 80 feet wide and 25 feet tall. What will be the equation of the parabolic shape of the gate?

Answer 1

1) the form of the equation may be written as y = A(X - Xo)(X - X1)

Where Xo and X1 are the two roots of the equation.


2) We can fix the system of coordinates so that the vertex is in the middle of the gate => Xo = - 40 and X1 = +40


=> y = A (X + 40) (X - 40) = A (X^2 - 1600) 


3) The height, at X = 0 is 25

=> A(0 - 1600) = 25


=> -1600A = 25 => A = -25 / 1600 = - 1/64


4) The equation is y =  - [1/64] (X^2 - 1600)


5) You can present it in different equivalent forms.

Some of those other forms are:

1) - 64y = (x^2 - 1600)

2) x^2 = - 64y + 1600

3) X^2 = - 64 (y - 25)