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Jerald jumped from a bungee tower. The equation that models his height in feet is [tex]h = -16t^2 + 729[/tex], where [tex]t[/tex] is the time in seconds.

For which interval of time is he less than 104 feet above the ground?

A. [tex]t \ \textgreater \ 6.25[/tex]
B. [tex]-6.25 \ \textless \ t \ \textless \ 6.25[/tex]
C. [tex]t \ \textless \ 6.25[/tex]
D. [tex]0 \leq t \leq 6.25[/tex]

Answer :

To determine the interval of time during which Jerald is less than 104 feet above the ground, we need to solve the inequality based on the equation of the height:

[tex]\[ h = -16t^2 + 729 \][/tex]

We want to find when the height [tex]\( h \)[/tex] is less than 104 feet:

[tex]\[ -16t^2 + 729 < 104 \][/tex]

1. Rearrange the inequality:

Subtract 104 from both sides:

[tex]\[ -16t^2 + 729 < 104 \][/tex]

[tex]\[ -16t^2 < 104 - 729 \][/tex]

Simplify:

[tex]\[ -16t^2 < -625 \][/tex]

2. Solve for [tex]\( t^2 \)[/tex]:

Divide both sides by -16. Remember, dividing or multiplying by a negative number flips the inequality sign:

[tex]\[ t^2 > \frac{625}{16} \][/tex]

Simplify the fraction:

[tex]\[ t^2 > 39.0625 \][/tex]

3. Find the values of [tex]\( t \)[/tex]:

We solve the equation [tex]\( t^2 = 39.0625 \)[/tex] to find the critical points.

Taking the square root of both sides, we get:

[tex]\[ t = \pm \sqrt{39.0625} \][/tex]

Calculating the square roots:

[tex]\[ t = \pm 6.25 \][/tex]

4. Determine the interval:

Since [tex]\( t^2 > 39.0625 \)[/tex], Jerald's height is less than 104 feet when [tex]\( t \)[/tex] is outside the range between -6.25 and 6.25:

[tex]\( t < -6.25 \)[/tex] or [tex]\( t > 6.25 \)[/tex]

Given that time [tex]\( t \)[/tex] in this context is non-negative (since it represents seconds after the jump starts), we only consider positive values, resulting in:

[tex]\[ t > 6.25 \][/tex]

Thus, Jerald is less than 104 feet above the ground for [tex]\( t > 6.25 \)[/tex] seconds.

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