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A creature on the moon throws a rock off a cliff. the height of the rock above the surface of the moon, in meters, t seconds after it is thrown is given by h(t) = -t^2 +8t +10. when does the rock hit the surface of the moon?

 Mar 3, 2021
 #1
avatar+117 
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Easier to understand: A creature on the moon throws a rock off a cliff. the height of the rock above the surface of the moon, in meters, \(t\) seconds after it is thrown is given by \(h(t) = -t^2 +8t +10\). when does the rock hit the surface of the moon?

 Mar 3, 2021
 #2
avatar+30781 
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When the rock hits the surface   h = 0

 

0 = -t^2 +8t + 10     use quadratic formula     a = -1    b = 8    c = 10    

 

\(t = {-b \pm \sqrt{b^2-4ac} \over 2a}\)       You will get TWO values of 't' ....throw out the negative value

 Mar 3, 2021

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