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Math Help - Need some basic algerbra help

  1. #1
    Junior Member Dergyll's Avatar
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    Need some basic algerbra help

    Sorry guys for posting such basic question but I can't find it anywhere.

    How fo you recognize a quadratic equation? I know about counting the degree and stuff but is there maybe a test that can be done to test each equation?

    Like for example: 7x+4xy-2x+5y Is this a quadratic?

    Oh and someone told me that xy=6 is also a quadratic...how is that? Because of degree?

    THanks guys
    Derg
    Last edited by Dergyll; November 7th 2006 at 01:40 PM.
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  2. #2
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    From MathWorld: "A quadratic equation is a second-order polynomial equation in a single variable x, ax^2+bx+c, where a \ne 0."

    I don't see how xy=6 is quadratic.
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Dergyll View Post
    Sorry guys for posting such basic question but I can't find it anywhere.

    How fo you recognize a quadratic equation? I know about counting the degree and stuff but is there maybe a test that can be done to test each equation?

    Like for example: 7x+4xy-2x+5y Is this a quadratic?

    Oh and someone told me that xy=6 is also a quadratic...how is that? Because of degree?

    THanks guys
    Derg
    I suppose you could call it quadratic if you define quadratic as being a second order equation. But I too had thought it was only a quadratic if it the expression was a polynomial.

    -Dan
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  4. #4
    Junior Member Dergyll's Avatar
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    Im thinking it depends on how you count the degrees, I've never fully grasped that idea of degrees though...How do you count degrees?

    How about the equation 7x+4xy-2x+5y, is it a quadratic? My teacher specifically said that xy=6 is a quadratic, something about a circle being involved...

    Any ideas guys?
    Thanks a bunch
    Derg
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  5. #5
    Junior Member Dergyll's Avatar
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    Got it

    This is how my teacher defined it as : A Equation with a degree of 2 is considered as a quadratic equation, so technically xy=6 can be written as
    x^1 time y^1 = 6 and the 1 degree from x and y add to be 2. But what exactly is degrees?

    So I guess 7x+4xy-2x+5y is a quadratic according this definition...

    Derg
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  6. #6
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    When you have a multivariable polynomial the degree is the sum of the exponents.

    Also, xy=7 is a rotated hyperbola, (second degree curve).
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  7. #7
    Junior Member Dergyll's Avatar
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    Sorry.

    So does this mean that xy=6 is a quadratic in definition? When I graphed it on my calculator (by dividing both sides my x and then graphing it) and found that it is 2 curved parabolas rotated, one in quadrant 2 and another in 4.

    Thanks for the help!
    Derg
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  8. #8
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    Quote Originally Posted by Dergyll View Post
    Sorry.

    So does this mean that xy=6 is a quadratic in definition?
    In that sense, yes.

    When I graphed it on my calculator (by dividing both sides my x and then graphing it) and found that it is 2 curved parabolas rotated, one in quadrant 2 and another in 4.
    It is not a pair of parabolas. It is a single hyperbola.
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