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5. [09.02]

The height of water shooting from a fountain is modeled by the function [tex]f(x) = -4x^2 + 24x - 29[/tex], where [tex]x[/tex] is the distance from the spout in feet. Complete the square to determine the maximum height of the path of the water. (2 points)

A. [tex]-4(x-3)^2 - 29[/tex]; The maximum height of the water is 3 feet.
B. [tex]-4(x-3)^2 - 29[/tex]; The maximum height of the water is 29 feet.
C. [tex]-4(x-3)^2 + 7[/tex]; The maximum height of the water is 7 feet.
D. [tex]-4(x-3)^2 + 7[/tex]; The maximum height of the water is 3 feet.

Sagot :

Let's solve this problem step-by-step in detail:

1. Starting with the given quadratic function:

[tex]\[ f(x) = -4x^2 + 24x - 29 \][/tex]

2. We aim to write this equation in vertex form, which is:

[tex]\[ f(x) = a(x-h)^2 + k \][/tex]

3. First, we need to factor out the coefficient of \(x^2\) from the first two terms:

[tex]\[ f(x) = -4(x^2 - \frac{24}{-4}x) - 29 \][/tex]

[tex]\[ f(x) = -4(x^2 - 6x) - 29 \][/tex]

4. Next, we complete the square inside the parentheses:

To complete the square:
- Take half the coefficient of \(x\), which is \(-6\), and square it.

Half of \(-6\) is \(-3\), and \((-3)^2\) is \(9\).

5. Add and subtract this square inside the parentheses:

[tex]\[ f(x) = -4(x^2 - 6x + 9 - 9) - 29 \][/tex]

[tex]\[ f(x) = -4((x - 3)^2 - 9) - 29 \][/tex]

6. Distribute the \(-4\) through the parentheses:

[tex]\[ f(x) = -4(x - 3)^2 + 4 \cdot 9 - 29 \][/tex]

[tex]\[ f(x) = -4(x - 3)^2 + 36 - 29 \][/tex]

[tex]\[ f(x) = -4(x - 3)^2 + 7 \][/tex]

7. Now, we have the function in vertex form:

[tex]\[ f(x) = -4(x - 3)^2 + 7 \][/tex]

8. The vertex of this function \((h, k)\) gives the maximum (or minimum) height of the parabolic path. In this case, since the coefficient of \((x - h)^2\) is negative (-4), the parabola opens downward, indicating a maximum point.

The vertex is \((3, 7)\), so the maximum height of the water is given by the \(k\) value, which is \(7\) feet.

Therefore, the correct answer is:

[tex]\[ -4(x - 3)^2 + 7 \][/tex]
The maximum height of the water is [tex]\(7\)[/tex] feet.