Question 459570
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The distance above the ground when the ball hits the ground is zero, so solve:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 128\ +\ 112t\ -\ 16t^2\ =\ 0]


for the positive root (it certainly didn't hit the ground <i>before</i> you threw it, right?).


The ball is at 128 feet at time 0 and at the time when the ball passes the top of the building on the way down.  So solve:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 128\ +\ 112t\ -\ 16t^2\ =\ 128]


One of the roots is 0, and we know what that means, so you can discard it.  The other root is your answer.


John
*[tex \LARGE e^{i\pi} + 1 = 0]
My calculator said it, I believe it, that settles it
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