The main cable of a suspension bridge forms a parabola, described by the equation [tex]\( y = a(x-h)^2 + k \)[/tex], where [tex]\( y \)[/tex] is the height in feet of the cable above the roadway, [tex]\( x \)[/tex] is the horizontal distance in feet from the left bridge support, [tex]\( a \)[/tex] is a constant, and [tex]\( (h, k) \)[/tex] is the vertex of the parabola.

Given:
- At a horizontal distance of [tex]\( 30 \)[/tex] ft, the cable is [tex]\( 15 \)[/tex] ft above the roadway.
- The lowest point of the cable is [tex]\( 6 \)[/tex] ft above the roadway and is a horizontal distance of [tex]\( 90 \)[/tex] ft from the left bridge support.

1. Which quadratic equation models the situation correctly?

[tex]\( y = 0.0025(x-90)^2 + 6 \)[/tex]

2. The main cable attaches to the left bridge support at a height of [tex]\( 26.25 \)[/tex] ft.

3. The main cable attaches to the right bridge support at the same height as it attaches to the left bridge support. What is the distance between the supports?



Answer :

To determine the distance between the left and right supports of the suspension bridge, we need to analyze the given information and deduce where the cable attaches to the supports.

* Given the quadratic equation of the parabola representing the cable:
[tex]\[ y = 0.0025(x - 90)^2 + 6 \][/tex]
where:
- [tex]\( y \)[/tex] is the height of the cable above the roadway in feet.
- [tex]\( x \)[/tex] is the horizontal distance from the left bridge support in feet.
- The vertex of the parabola [tex]\( (h, k) = (90, 6) \)[/tex] is the lowest point of the cable.

* The cable attaches to the bridge supports at a height of [tex]\( 26.25 \)[/tex] feet.

To find the points where the cable attaches to the supports, we need to determine the values of [tex]\( x \)[/tex] when [tex]\( y = 26.25 \)[/tex].

1. Starting with the equation:
[tex]\[ 26.25 = 0.0025(x - 90)^2 + 6 \][/tex]

2. Subtract 6 from both sides to isolate the quadratic term:
[tex]\[ 20.25 = 0.0025(x - 90)^2 \][/tex]

3. Divide both sides by 0.0025 to solve for [tex]\((x - 90)^2\)[/tex]:
[tex]\[ 8100 = (x - 90)^2 \][/tex]

4. Take the square root of both sides to solve for [tex]\( x - 90 \)[/tex]:
[tex]\[ x - 90 = \pm 90 \][/tex]

5. Solve for [tex]\( x \)[/tex] in both cases to find the points of attachment:
- For [tex]\( x - 90 = 90 \)[/tex]:
[tex]\[ x = 180 \][/tex]
- For [tex]\( x - 90 = -90 \)[/tex]:
[tex]\[ x = 0 \][/tex]

The cable attaches to the left support at [tex]\( x = 0 \)[/tex] and to the right support at [tex]\( x = 180 \)[/tex].

6. Calculate the distance between the supports:
[tex]\[ \text{Distance between supports} = 180 - 0 = 180 \text{ feet} \][/tex]

Therefore, the distance between the left and right supports is 180 feet.