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Math Help - [SOLVED] SAT math page 656

  1. #1
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    [SOLVED] SAT math page 656

    In the figure below, PQRS is a rectangle, and points Q and R lie on the graph of y=ax^2, where a is a constant. If the perimeter of PQRS is 10, what is the value of a?

    From the graph I got that the length of the rectangle is 3 and the width is 2. Is this correct? I don't know what to do next. Thanks in advance
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    Quote Originally Posted by fabxx View Post
    In the figure below, PQRS is a rectangle, and points Q and R lie on the graph of y=ax^2, where a is a constant. If the perimeter of PQRS is 10, what is the value of a?

    From the graph I got that the length of the rectangle is 3 and the width is 2. Is this correct? I don't know what to do next. Thanks in advance
    You know that the distance PQ is 3.
    The coordinates of P are (-1;0). Since PQ is parallel to the y axis, their x-ordinate are the same : -1.
    And the distance PQ will be the difference between their y-ordinates.
    So point Q has coordinates (-1;3)

    Now, substitute them into y=ax˛ to get a.
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    is it like this?

    Because y=3 and x=(-1)
    and because y=ax^2
    so therefore 3=a(-1)^2
    so a=3?

    Thanks in advance
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  4. #4
    Moo
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    Quote Originally Posted by fabxx View Post
    is it like this?

    Because y=3 and x=(-1)
    and because y=ax^2
    so therefore 3=a(-1)^2
    so a=3?

    Thanks in advance
    Yes it is
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    Thanks Moo! You're very helpful!
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