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** -x**^{2}** + 4x + 32**

Factor out -1

-(x^{2}-4x-32)=0

Factor

-(X-8)(x+4)=0

Set each equal to zero

x-8=0. X=8

If you set x+4=0 you get x=-4 which we can disregard since we cannot have negative time

So the answer is 8 seconds

Grace J.

asked • 04/01/19The speed of a firework x seconds after lighting up can be modeled with the expression -x^{2 }+ 4x + 32. How long after lighting the firework does the firework stop moving?

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Factor out -1

-(x^{2}-4x-32)=0

Factor

-(X-8)(x+4)=0

Set each equal to zero

x-8=0. X=8

If you set x+4=0 you get x=-4 which we can disregard since we cannot have negative time

So the answer is 8 seconds

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