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Math Help - quadratics

  1. #1
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    quadratics

    a ball is thrown straight up its height h(metres) after t seconds is given, h=-5t^2+10t+2. To the nearest tenth of a second, when is the ball 6m above the ground? Explain why there is two answers. Help me please
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  2. #2
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    Hello, mcinnes!

    It's simple algebra . . . Exactly where is your difficulty?


    A ball is thrown straight up.
    Its height h in metres after t seconds is: . h \:=\:-5t^2+10t+2

    To the nearest tenth of a second, when is the ball 6m above the ground?
    Explain why there is two answers.
    The question is: When is h = 6 ?

    We have: . -5t^2 + 10t + 2 \:=\:6 \quad\Rightarrow\quad 5t^2 - 10t +4 \:=\:0

    Quadratic Formula: . t \;=\;\frac{10 \pm\sqrt{20}}{10} \;=\;\frac{5\pm\sqrt{5}}{5} \;\approx\;\begin{Bmatrix}1.4 \\ 0.6\end{Bmatrix} seconds.

    It attains a height of 6 meters on the way up and on the way down.

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  3. #3
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    im doing math on my own, and need to see how some questions are answered, with all the work, and what not, so i can do them on all the other questions i have, with this one, i dont get the two answer part of it, i wouldnt mind knowing why or how there is two answers:P
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  4. #4
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    Quote Originally Posted by mcinnes View Post
    im doing math on my own, and need to see how some questions are answered, with all the work, and what not, so i can do them on all the other questions i have, with this one, i dont get the two answer part of it, i wouldnt mind knowing why or how there is two answers:P
    If you graphed the equation you would find it is a parabola. He gave you the (physical) reason why there are two answers...If you throw a ball in the air it goes up...reaches a max height...and comes back down.
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