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Math Help - Writing Quadratic Functions

  1. #1
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    Writing Quadratic Functions

    This is also driving my crazy. I'm asked to write in standard form of the quadratic function. It gives me a picture of a parabola and 3 points, 1 of them is the vertex.

    Here's an example:


    I don't get it at all.
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  2. #2
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by BeSweeet View Post
    This is also driving my crazy. I'm asked to write in standard form of the quadratic function. It gives me a picture of a parabola and 3 points, 1 of them is the vertex.

    Here's an example:


    I don't get it at all.
    Recall that the standard form is f(x)=a(x-h)^2+k, where (h,k) is the vertex.

    Then plug in any point that is given to you in the graph above to find a.

    Can you try to take it from here?
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  3. #3
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    It wants me to write it in standard form, not solve for a... Or am I missing something?

    Here's what the problem looks like:
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  4. #4
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    Quote Originally Posted by BeSweeet View Post
    It wants me to write it in standard form, not solve for a... Or am I missing something?
    you need to solve for "a" to complete the equation.
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  5. #5
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    So I can pick one of those two points? Trying it now.
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  6. #6
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    Awesome! Definitely have this stuff figured out now. Thanks to everyone who helped with those quick responses!!
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  7. #7
    Super Member 11rdc11's Avatar
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    Ok I'm not trying to hijack this post but got a quick question.

    Using Sum and Product of the roots you can get the equation but how would you know which is correct without using the graph

    Sum = 0
    Product = -1

    so

    x^2 -1 which is incorrect

    or

    x^2 + 1 which is correct
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  8. #8
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    Quote Originally Posted by 11rdc11 View Post
    Ok I'm not trying to hijack this post but got a quick question.

    Using Sum and Product of the roots you can get the equation but how would you know which is correct without using the graph

    Sum = 0
    Product = -1

    so

    x^2 -1 which is incorrect

    or

    x^2 + 1 which is correct
    correction ... 1-x^2
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  9. #9
    Super Member 11rdc11's Avatar
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    Quote Originally Posted by skeeter View Post
    correction ... 1-x^2
    oops lol thanks. Otherwise I have imaginary numbers. Forgot to put the negative infront of x^2 so the graph opens downward. But skeeter how would I know that -x^2 +1 is the graph and not x^2 -1 just using the formula x^2 - Sx + P
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  10. #10
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    Quote Originally Posted by 11rdc11 View Post
    oops lol thanks. Otherwise I have imaginary numbers. Forgot to put the negative infront of x^2 so the graph opens downward. But skeeter how would I know that -x^2 +1 is the graph and not x^2 -1 just using the formula x^2 - Sx + P
    you can't know w/o additional info ... both have the same sum/product of roots.
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  11. #11
    Super Member 11rdc11's Avatar
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    Quote Originally Posted by skeeter View Post
    you can't know w/o additional info ... both have the same sum/product of roots.
    O ok thanks that is what I thought
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