SOLUTION: I would greatly appreciate any help on the following problem: An object is projected upward from the top of a tower. Its distance in feet above the ground after t seconds is given

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: I would greatly appreciate any help on the following problem: An object is projected upward from the top of a tower. Its distance in feet above the ground after t seconds is given by s(t)=-16t^2+64t+80. How many seconds will it take to reach ground level? This question is from textbook

Answer by aaaaaaaa(138)   (Show Source): You can put this solution on YOUR website!
Ground level is 0 feet, so it's a quadratic equation:

Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation (in our case ) has the following solutons:



For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=9216 is greater than zero. That means that there are two solutions: .




Quadratic expression can be factored:

Again, the answer is: -1, 5. Here's your graph:


We only want the positive solution, which is 5 seconds.
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