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

Question 236860: 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 Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
Starting with the given function:
you are being asked..."at what time, t, will h(t) = 240 ft."
So you set h(t) = 240 and solve for t.
Subtract 240 from both sides and rearrange a bit.
Now you have a quadratic equation that can be solved by various methods.
I would factor -16 first just to simplify the calculations a bit.
Notice the change of signs when we factored the -16!
Now, from the zero product rule, you get:
This can be solved by factoring.
Apply the zero product rule again.
or so that...
or
Why are there two answers?
On the way up, the object will reach 240 feet in 3 seconds (t = 3).
On the way down, the object will again pass the 240-foot level in 5 seconds (t = 5).
Does this all make sense to you?
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