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anonymous

  • 5 years ago

A projectile is fired straight up from ground level. After t seconds it's height is above the ground is h feet where h=-16t^2+144t. For what time period is the projectile at least 288 ft off the ground?

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  1. anonymous
    • 5 years ago
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    Plug in 288 for h, move it over to the right side and do the quadratic formula to solve for t. You will get 2 times, in between and including those times will give you the period it is at least 288 ft off the ground.

  2. anonymous
    • 5 years ago
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    so you end up with an equation like this 0=-16t^2+144t-288??

  3. anonymous
    • 5 years ago
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    hi radar.

  4. radar
    • 5 years ago
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    You can simplify this and not need to use the quadratic. \[288=-16t ^{2}+144t\] Divide through by 16 getting 18=-t^2 + 9t

  5. anonymous
    • 5 years ago
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    so you end up with 3 and 6?

  6. radar
    • 5 years ago
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    \[t ^{2}-9t+18=0\] Is what you would get after rearranging the equation Now you have something you can easily factor. Hi Raslk2kl1

  7. radar
    • 5 years ago
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    Yes now I don't know if that means it was above 288 feet for the time 3 thru 6 seconds or not. can you figure that out

  8. anonymous
    • 5 years ago
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    Yes, the way I enter the answers seems like it is between 3 and 6 seconds

  9. radar
    • 5 years ago
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    Fine, good luck.

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