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Math Help - Proportions

  1. #1
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    Proportions

    1. 3/x=x/?

    2. 3/?=?/10

    3. 13/z=z/?

    4. ?/y=y/10

    5. 10/?=?/13

    6. 13/?=?/3

    These proportions are very strange to me, but its the way the book has it layed out.

    Directions say use theorems 7.2 and 7.3 which make no sense to me, but here they are:

    7.2 In a right triangle, the length of the altitude to the hypotenuse is the geometric mean between the lengths of the two segments on the hypotenuse.

    7.3 In a right triangle with an altitude to the hypotenuse, each leg is the geometric mean between the sum of the squares of the lengths of the legs.
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  2. #2
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    i guess my question is how do you find the ? for a problem like 3/x=x/?

    once i know how to find the ? i can take it from there
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by OzzMan View Post
    i guess my question is how do you find the ? for a problem like 3/x=x/?

    once i know how to find the ? i can take it from there
    I would replace the ? with a variable, say y:
    \frac{3}{x} = \frac{x}{y}

    Multiply both sides by xy:
    3y = x^2 <--Otherwise known as "cross-multiplication."

    y = \frac{x^2}{3}

    You can do this kind of thing with all of them.

    -Dan
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  4. #4
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    Wow another easy problem. Thanks for the help. The book was dumb imo to have ? marks instead of lettered variables.
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  5. #5
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    nvm these problems arent done by cross multiplication. i checked the answer in the back of the book and they got non variable answers for both variables. so i really have no idea now.
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  6. #6
    Bar0n janvdl's Avatar
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    Quote Originally Posted by OzzMan View Post
    nvm these problems arent done by cross multiplication. i checked the answer in the back of the book and they got non variable answers for both variables. so i really have no idea now.
    What answer does the book give?
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  7. #7
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    the books answer for the first one is 10, x=square root of 30

    which im assuming the 10 is for the ?

    but how are these answers correct. i see no logical way of them being correct. anyone know ?
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  8. #8
    Bar0n janvdl's Avatar
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    Quote Originally Posted by OzzMan View Post
    the books answer for the first one is 10, x=square root of 30

    which im assuming the 10 is for the ?

    but how are these answers correct. i see no logical way of them being correct. anyone know ?
    No i cannot see why it would be those answers specifically either.
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  9. #9
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    yes biggest question is how did they get 10 for the ? makes no sense.
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  10. #10
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    Sorry to post again on this post but if anyone knows how to do this, could you help me out. I'm really lost with this. Mostly how they solve for the ? in the first one.
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  11. #11
    Bar0n janvdl's Avatar
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    Quote Originally Posted by OzzMan View Post
    Sorry to post again on this post but if anyone knows how to do this, could you help me out. I'm really lost with this. Mostly how they solve for the ? in the first one.
    You'll get an infraction for bumping

    No, honestly I cannot see how they got those values.
    These equations can be satisfied with just about any value. (Although it seems it has to be only positive values)

    EDIT: Talk to your teacher about this?
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  12. #12
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    Well this is my brothers homework and its from his geometry book. I'm just curious.
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  13. #13
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by OzzMan View Post
    Well this is my brothers homework and its from his geometry book. I'm just curious.
    If the solution for #1 does not contain an x then there is information missing.

    These cannot be done as stated. (As several people have now informed you.)

    -Dan
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