SOLUTION: the height of an object projected upward from ground level is given by h+-16t^2+128t where h is in feet and t is time in seconds. when will the object be 240 feet above ground leve

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Question 236861: the height of an object projected upward from ground level is given by h+-16t^2+128t where h is in feet and t is time in seconds. when will the object be 240 feet above ground level ...

please help i dont understand
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!
the height of an object projected upward from ground level is given by h=-16t%5E2%2B128t where h is in feet and t is time in seconds. when will the object be 240 feet above ground level ...
please help i dont understand

h=-16t%5E2%2B128t

Substitute 240 ft as the height h in the equation:

240=-16t%5E2%2B128t

Get 0 on the right:  

16t%5E2-128t%2B240=0

Divide every term by 16

%2816t%5E2%29%2F16-%28128t%29%2F16%2B240%2F16=0

t%5E2-8t%2B15=0

Factor the left side:

%28t-3%29%28t-5%29=0

Set each factor = 0

Setting t-3=0%7D%7D%0D%0A++++++++%7B%7B%7Bt=3 

Setting t-5=0
        t=5

There are two solutions, because the
object will be exactly 240 feet above
the ground on its way UP exactly 3 
seconds after it is projected upward. 
Then it will be 240 feet above the ground 
again on its way back DOWN 5 seconds 
after it is projected upward.  So the 
answer is both 3 seconds and 5 seconds
after it is projected upward.

Edwin