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A flying objects height in the sky can be represented by the equation d=30+vt+4t^2 where d is the height in feet , v is the velocity in feet per second, and t is the time in seconds. How long has the flying object been traveling if it has velocity of 8 feet per second and has risen to a height of 126 feet?

A: 4 seconds
B: 6 seconds
C: 8 seconds
D: 16 seconds

Respuesta :

znk

Answer:

4 s  

Step-by-step explanation:

d = 30 + vt + 4t²

v = 8 ft/s; d = 126 ft

             126 = 30 + 8t + 4t²     Subtract 126 from each side

4t² + 8t - 96 = 0                        Divide each side by 4

 t² + 2t – 16 = 0                        Factor the equation

(t + 6)(t – 4) = 0

t + 6 =  0     t – 4 = 0

     t = -6           t = 4

We reject the negative time, so t = 4.

The object has been travelling for 4 s.

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