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Math Help - intersection of lines

  1. #1
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    intersection of lines

    How would you determine if lines intersected or not

    if the lines were something like

    y=-x-2

    and

    y=x^2+2-4
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  2. #2
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    Well since you have two expressions involving x's and y's you can put them together.

    y=-x-2 and y=x^2+2x-4 so y=-x-2=x^2+2x-4 by equating the y's.

    So you need to solve -x-2=x^2+2x-4 to get the x co-ordinate. The y co-ordinate can then be found by substituting this x value into one of the two equations (they should give the same answer if you've done it right!).
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  3. #3
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    Quote Originally Posted by Showcase_22 View Post
    Well since you have two expressions involving x's and y's you can put them together.

    y=-x-2 and y=x^2+2x-4 so y=-x-2=x^2+2x-4 by equating the y's.

    So you need to solve -x-2=x^2+2x-4 to get the x co-ordinate. The y co-ordinate can then be found by substituting this x value into one of the two equations (they should give the same answer if you've done it right!).
    would i just collect like terms and factor or how would i solve that?
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  4. #4
    Super Member Showcase_22's Avatar
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    Exactly!

    <br />
-x-2=x^2+2x-4<br />

    Here's the first step: x^2+2x+x-4+2=0.
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  5. #5
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    Quote Originally Posted by william View Post
    How would you determine if lines intersected or not

    if the lines were something like

    y=-x-2

    and

    y=x^2+2-4
    As far as I know y = x^2 + 2x - 4 is not a line... Its a parabola
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  6. #6
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    Quote Originally Posted by Isomorphism View Post
    As far as I know y = x^2 + 2x - 4 is not a line... Its a parabola
    AH YES! thank you i could simply graph both and see where they intersect,if anywhere
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  7. #7
    Super Member Showcase_22's Avatar
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    Simultaneous equations are faster than just graphing them.

    What if you have two lines that intersect at (100,1000000)? It would be very hard to draw a graph for that!
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