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If an object is propelled upward from a height of s feet at an initial velocity of v feet per second, then its height h after t seconds is given by the equation h = -16t^2+vt+s, where h is in feet. If the object is propelled from a height of 12 feet with an initial velocity of 64 feet per second, it's height h is given by the equation h = -16t^2+64t+12. After how many seconds is the height 72 feet?

Respuesta :

Answer:

The object first reaches 72 feet after 1.5 seconds; it is this height again after 2.5 seconds.

Step-by-step explanation:

To find the amount of time it takes to reach 72 feet, we solve the equation

72 = -16t² + 64t + 12

To solve this, we will set it equal to 0 by subtracting 72 from each side:

72-72 = -16t² + 64t + 12 - 72

0 = -16t² + 64t - 60

Next we will use the quadratic formula to solve this: