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Math Help - qaudratic eqautions

  1. #1
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    qaudratic eqautions

    X-2=10
    X(SQAURED)+Y(SQAURED)=20

    I cant seem to get the formula to work...keeps on coming out uneven!!!
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by ENNO View Post
    X-2=10
    X(SQAURED)+Y(SQAURED)=20

    I cant seem to get the formula to work...keeps on coming out uneven!!!
    check your question again. it makes no sense to write x - 2 = 10. why not just write x = 12?
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  3. #3
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    Quote Originally Posted by Jhevon View Post
    check your question again. it makes no sense to write x - 2y = 10. why not just write x = 12?
    because I just took it straight from the book...this doesnt help my problem in any way!
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by ENNO View Post
    because I just took it straight from the book...this doesnt help my problem in any way!
    ok. i think you need to provide more info. because i don't see what you want to do here. it seems you want to solve the equations simultaneously, but then the solution for x is given in the first equation which makes the problem trivial. simply substitute x = 12 into the second equation to solve for y. the problem is stupid, unless i am misinterpreting the directions and/or you made a typo
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    Quote Originally Posted by Jhevon View Post
    ok. i think you need to provide more info. because i don't see what you want to do here. it seems you want to solve the equations simultaneously, but then the solution for x is given in the first equation which makes the problem trivial. simply substitute x = 12 into the second equation to solve for y. the problem is stupid, unless i am misinterpreting the directions and/or you made a typo
    yes I did...it is a simultaneous eqaution...sorry bout that!

    And alos it is a 2y...
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by ENNO View Post
    yes I did...it is a simultaneous eqaution...sorry bout that!

    And alos it is a 2y...
    so you did make a typo!

    well, anyway. keep the same game plan. from the first equation then, x = 10 + 2y

    plug this in for x in the second equation and solve for y. then you can find x
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  7. #7
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    Quote Originally Posted by Jhevon View Post
    so you did make a typo!

    well, anyway. keep the same game plan. from the first equation then, x = 10 + 2y

    plug this in for x in the second equation and solve for y. then you can find x
    Thats my problem,

    I can work it out into a qaudratic formula but it doesnt work out!


    80-40y-5y(sqaured)=0....when I plug it into the qaudratic formula i get crazy answers!
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  8. #8
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by ENNO View Post
    Thats my problem,

    I can work it out into a qaudratic formula but it doesnt work out!


    80-40y-5y(sqaured)=0....when I plug it into the qaudratic formula i get crazy answers!
    ok, we have:

    x - 2y = 10 .................(1)
    x^2 + y^2 = 20 ...........(2)

    From (1), x = 10 + 2y, plug this into (2), we get:

    (10 + 2y)^2 + y^2 = 20

    \Rightarrow 100 + 40y + 4y^2 + y^2 = 20

    \Rightarrow 5y^2 + 40y + 80 = 0

    \Rightarrow y^2 + 8y + 16 = 0

    this is a perfect square, we don't even need the quadratic formula here

    \Rightarrow (y + 4)^2 = 0

    \Rightarrow y = -4

    now continue
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  9. #9
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    Quote Originally Posted by Jhevon View Post
    ok, we have:

    x - 2y = 10 .................(1)
    x^2 + y^2 = 20 ...........(2)

    From (1), x = 10 + 2y, plug this into (2), we get:

    (10 + 2y)^2 + y^2 = 20

    \Rightarrow 100 + 40y + 4y^2 + y^2 = 20

    \Rightarrow 5y^2 + 40y + 80 = 0

    \Rightarrow y^2 + 8y + 16 = 0

    this is a perfect square, we don't even need the quadratic formula here

    \Rightarrow (y + 4)^2 = 0

    \Rightarrow y = -4

    now continue
    I worked it out and got X=18...am I right?
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  10. #10
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by ENNO View Post
    I worked it out and got X=18...am I right?
    no
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  11. #11
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    Quote Originally Posted by ENNO View Post
    I worked it out and got X=18...am I right?
    You're nearly right ....... It's not 10 plus 8 .....
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