Keep in mind that when $h=0$ , this is the same height for both when the model rocket takes off and lands, so when the rocket lands, time is positive. Thus:

$h=-4t^2+24t+13\\\\0=-4t^2+24t+13\\\\t=\frac{-b\pm\sqrt{b^2-4ac}}{2a}\\ \\t=\frac{-24\pm\sqrt{24^2-4(-4)(13)}}{2(-4)}\\ \\t=\frac{-24\pm\sqrt{576+208}}{-8}\\\\t=\frac{-24\pm\sqrt{576+208}}{-8}\\\\t=\frac{-24\pm\sqrt{784}}{-8}\\\\t=\frac{-24\pm28}{-8}\\\\t=\frac{-24-28}{-8}\\ \\t=\frac{-52}{-8}\\ \\t=\frac{52}{8}\\\\t=6.5$

So, the amount of seconds that the model rocket stayed above the ground since it left the platform is 6.5 seconds

5 0

2 years ago

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What is the square root of -1?

Alchen [17]

Answer: √−1=i.

Step-by-step explanation: When we say that the square root of a negative number "doesn't exist", we mean that there is no real number solution. However, if we consider complex numbers, we then get a solution to √−1=i.

4 0

3 years ago

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Need help test coming soon can some help!?<br><br><br> Please

Paha777 [63]

Answer:

81 square metres is right anser follow me plse

4 0

2 years ago

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