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Thread: Parabola question???

  1. #1
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    Unhappy Parabola question???

    My question is kind of basic and stupid... but how in the world do you graph THIS question??
    I need someone to walk me through it.

    y = x^2 - 3x - 4

    Should i factorise it or what?? It seems like iI should know this question but i don't.
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  2. #2
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    Re: Parabola question???

    Factorisation gives y=(x-4)(x+1), thus the roots are x=-1 and x=4. Further the minimum is attained at x=3/2 (half way between the roots) and y(3/2) = -25/4. Now draw a nice parabola through (-1,0) , (3/2,-25/4) and (4,0).
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  3. #3
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    Re: Parabola question???

    Yep that looks right to me. If you have a basic calculator you can put it into table mode, and input the equation. It then gives you the results for any input of $\displaystyle x$.

    However, it is easy to calculte without a calculator. Just get take values for $\displaystyle x$, say -5, 0, 5, and stick them into the equation. Work it out, and you will obtain a table of results.

    ie.
    $\displaystyle y=x^2-3x-4$

    Take $\displaystyle x=0$

    then, $\displaystyle y=0^2-(3\times0)-4$
    Therefore, $\displaystyle y=-4$

    Do the same for the other values, and then you can plot them.
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  4. #4
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    Re: Parabola question???

    hi would I do something similar to solve equations such as

    y=-3x+2

    and

    y=2x^2-7x-4

    dave
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  5. #5
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    Re: Parabola question???

    Then start your own thread. Do not "hijack" someone else's thread to ask separate questions.
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  6. #6
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    Re: Parabola question???

    sorry, I`ll do it now
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