The height h (in feet) above the water of a cliff diver is modeled by h=−16t2+8t+80 , where t is the time (in seconds). How long is the diver in the air?

Respuesta :

The height above the water is h = -16t² + 8t + 80.

When the diver is above the water, h > 0.
Solve the equation
-16t² + 8t + 80 = 0

Divide through by -8.
2t² - t - 10 = 0

Factorize.
(2t - 5)(t + 2 ) = 0
t = 2.5 or t = 2
Reject negative time, so that t = 2.5 seconds.
Therefore the time the diver is above the water is 2.5 sec.

Answer: 2.5 seconds

Solving the quadratic equation, it is found that the diver was in the air for 2 seconds.

The height of the diver after t seconds is given by:

[tex]h(t) = -16t^2 + 8t + 80[/tex]

He is in the air until [tex]h(t) = 0[/tex], hence:

[tex]-16t^2 + 8t + 80 = 0[/tex]

[tex]16t^2 - 8t - 80 = 0[/tex]

Which is a quadratic equation with coefficients [tex]a = 16, b = -8, c = -80[/tex]. Then:

[tex]\Delta = (-8)^{2} - 4(-16)(80) = 5184[/tex]

[tex]x_{1} = \frac{-8 + \sqrt{5184}}{32} = 2[/tex]

[tex]x_{2} = \frac{-8 - \sqrt{5184}}{32} = -2.5[/tex]  

Time is a positive measure, hence we take the positive solution, which means that the diver was in the air for 2 seconds.

A similar problem involving the solution of a quadratic equation is given at https://brainly.com/question/24764843