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December 20, 2014

December 20, 2014

Posted by **K.** on Tuesday, April 10, 2007 at 1:24pm.

I know that the conjugates are 2+i and -the square root of five, but when I multiply it comes out wrong.

not sure

A toy rocket is launched from the ground level with an initial vertical velocity of 96ft/s. After how many seconds will the rocket hit the ground?

In order to have your "simple polynomial function" I assume you want only rational coefficients.

For that to happen the zeros of 2-i and √5 must indeed have conjugate partner factors.

to get your given zeros included, the function must be

f(x) = (x-2-i)(x-2+i)(x^2 - 5)(x + 2)

I will leave the expansion up to you.

Hint: the first two factors expanded should have given you x^2 - 4x + 5

I don't usually work with non-metric units but I recall that the equation that would describe the height of this toy rocket would be

h = -16t^2 + 96t where t is seconds, and h is the height in feet

you want that height to be zero, so

0 = -16t^2 + 96t

16t^2 - 96t = 0

t(16t - 96)=0

so t=0 or t=6

the t=0 of course gives you the initial height, and

t=6 seconds would be the answer to your question.

Thank you so much for taking the time to help me with this problem. It was so nice of you!

I thought that how you told me is the way to set it up, but the mult. of the factors is what gives me trouble. In the answer, should there be square roots and "i"s? In your function I think you left out x^+5, is that right? I need more help!!)

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