SOLUTION: HELP PLEASE!!!!! If a stone is tossed from the top of a 170 meter building, the height of the stone as a function of time is given by h(t) = -9.8t^2 – 10t + 170, where t is in se

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Question 410027: HELP PLEASE!!!!!
If a stone is tossed from the top of a 170 meter building, the height of the stone as a function of time is given by h(t) = -9.8t^2 – 10t + 170, where t is in seconds, and height is in meters. After how many seconds will the stone hit the ground? Round to the nearest hundredth’s place; include units in your answer.
Answer by nerdybill(7384)   (Show Source): You can put this solution on YOUR website!
simply set h(t) to zero and solve for t:
h(t) = -9.8t^2 – 10t + 170
0 = -9.8t^2 – 10t + 170
0 = 9.8t^2 + 10t - 170
0 = 4.9t^2 + 5t - 85
applying the quadratic formula gives you:
t = {3.69, -4.71}
we can throw out the negative solution leaving:
t = 3.69 seconds
.
Details of the quadratic follows:
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=1691 is greater than zero. That means that there are two solutions: .




Quadratic expression can be factored:

Again, the answer is: 3.68589493774532, -4.70630310101063. Here's your graph:
= 0

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