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anonymous

  • one year ago

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  1. anonymous
    • one year ago
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    please explain too.

  2. welshfella
    • one year ago
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    take any point on the parabola (x0,y0) then the distance between this point and the focus is given by sqrt[(x0 - 2)^2 + (y0 - 0)^2 and distance of the point from the directrix = 12

  3. welshfella
    • one year ago
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    - sorry that distance from directrix is |y0 - 12|

  4. welshfella
    • one year ago
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    so as the distance from the focus = distance from the directrix ( definition of a parabola) we have sqrt[(x0 - 2)^2 + (y0 - 0)^2 = (0 -12) simplify this to get the required equation

  5. welshfella
    • one year ago
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    sorry - another typo its sqrt[(x - 2)^2 + (y - 0)^2] = (y -12)

  6. welshfella
    • one year ago
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    - I change x0 and y0 to x and y

  7. welshfella
    • one year ago
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    squaring both sides (x - 2)^2 + y^2 = (y - 12)^2 x^2 - 4x + 3 + y^2 = y^2 - 24y + 144 can you continue from here?

  8. anonymous
    • one year ago
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    Could you go all the way please?

  9. anonymous
    • one year ago
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    gave you best response

  10. welshfella
    • one year ago
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    x^2 - 4x + 4 + y^2 = y^2 - 24y + 144 x^2 - 4x - 140 = -24y y = (-1/24)x^2 + (1/6)x - 35/6 = 0

  11. anonymous
    • one year ago
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    thanks.

  12. welshfella
    • one year ago
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    I'm making a lot of typos today so I cant guarantee the answer but the method is right!

  13. anonymous
    • one year ago
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    yeah its an answer could you help me with one more

  14. welshfella
    • one year ago
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    no sorry gtg right now

  15. welshfella
    • one year ago
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    I'm still not happy with that result

  16. anonymous
    • one year ago
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    what result?

  17. welshfella
    • one year ago
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    AH! the distance for directrix is |x - (-12)| = |x + 12| so we have (x - 2)^2 + y^2 = y^2 + 24x + 144 x^2 - 4x + 4 + y^2 = y^2 + 24y + 144 x^2 - 4x - 144 + 4 = 24x y = (1/24)x^2 - (1/6)x - 144/24 = 0 y = (1/24)x^2 - (1/6)x - 35/6 = 0 is the correct answer

  18. anonymous
    • one year ago
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    http://openstudy.com/study#/updates/55b3b8b7e4b071e6530e1ca4 \

  19. welshfella
    • one year ago
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    the only problem with that is its not one of the options but I'm sure its correct

  20. welshfella
    • one year ago
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    I'll check with wolfram alpha

  21. anonymous
    • one year ago
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    lol wolfram

  22. welshfella
    • one year ago
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    http://www.wolframalpha.com/input/?i=equation+of+a+parabola+with+focus+%282%2C0%29+and+directrix+y+%3D+-12 there you go its correct

  23. anonymous
    • one year ago
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    okay

  24. anonymous
    • one year ago
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    come over here http://openstudy.com/study#/updates/55b3b8b7e4b071e6530e1ca4

  25. welshfella
    • one year ago
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    so there must be a typo in one of the choices looks like its C - which has 2 plus instead 2 negatives

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