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Thread: One for the geniuses out there...

  1. #1

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    One for the geniuses out there...

    You are given only this information:

    x + y + z = 4
    x2 + y2 + z2 = 6
    xyz = 3

    You are required to determine a numerical value for:

    x3 + y3 + z3

    No fancy stuff, just algebraic manipulation... I couldn't figure it out so anyone who can point me in the right direction, please relieve me of this.

  2. #2
    Lively Member mmiill's Avatar
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    !

    that is so easy!!!

    (x+y+z)^2=x^2+y^2+z^2+2(xy+xz+yz)=16

    x^2+y^2+z^2=6

    => xy+yz+xz=5

    now

    (xy+yz+zx)*(x+y+z)=x^2y+xyz+zx^2+xy^2
    +y^2z+zxy+xyz+yz^2+z^2x =
    x^2y+zx^2+xy^2+y^2z+yz^2+z^2x+3*xyz=20

    A=x^2y+zx^2+xy^2+y^2z+yz^2+z^2x=11
    A=11
    now

    (x^2+y^2+z^2)(x+y+z)=
    x^3+y^3+z^3 +A =24

    and
    x^3+y^3+z^3 =13

    SEE YA

    mm

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  4. #4
    Fanatic Member bugzpodder's Avatar
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    how did u do these images, NotLKH?
    Massey RuleZ! ^-^__Cheers!__^-^ Massey RuleZ!


    Did you know that...
    The probability that a random rational number has an even denominator is 1/3 (Salamin and Gosper 1972)? This result is independently verified by me (2002)!

  5. #5

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    And part 2...

    Yeah thanks a lot, as soon as I read your first lines I realized I'd missed the obvious way of doing it, hehe.

    Now for part 2:

    Given the drawing, find X:
    I had a 5 minute stab at this and couldn't be arsed to try any harder...
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  6. #6
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    its easy to do,hehe

  7. #7
    Fanatic Member bugzpodder's Avatar
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    what are these lines? medians? if its random lines i doubt it can be solved.
    Massey RuleZ! ^-^__Cheers!__^-^ Massey RuleZ!


    Did you know that...
    The probability that a random rational number has an even denominator is 1/3 (Salamin and Gosper 1972)? This result is independently verified by me (2002)!

  8. #8

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    They are in fact, random. You are given EXACTLY what I am. The question gives that exact diagram and says "Find the area x." I think it can be done but I don't have the time to try and work it out for myself... also I can't be arsed
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  9. #9
    pathfinder NotLKH's Avatar
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    It looks to me a bit trig intensive, but definetely do-able.
    Too bad I don't have the time.

    Here's an angle map of the problem I'd use if I did have time:

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  10. #10
    Fanatic Member Gandalf_Grey_'s Avatar
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    is this an equalateral, scalene or isocolese triangle? or do you not have that information?

  11. #11

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    You only get EXACTLY what I posted: that drawing and the quote that goes with it. You would have to assume that it's scaline I suppose...
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  12. #12

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    I just spent 5 minutes thinking and worked this out....
    So now I need the area A
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  13. #13
    Fanatic Member bugzpodder's Avatar
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    Massey RuleZ! ^-^__Cheers!__^-^ Massey RuleZ!


    Did you know that...
    The probability that a random rational number has an even denominator is 1/3 (Salamin and Gosper 1972)? This result is independently verified by me (2002)!

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