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# Question

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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
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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
+34328
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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