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Quadratic equations

  1. Oct 23, 2004 #1
    hey there reader

    i have:
    y=3x+11
    y=2xsquared+2x+5

    i have to solve these as they are represent a straight line and a curve respectively. so far i have:

    3x+11=2xsquared+2x+5 at the intersection

    ;2xsquared-x-6=0

    i factorised this and checked it to make sure it matched the above equation:

    (2x+4)(x-2.5)

    when i multiplied it out to check it i got: 2xsquared-x-6=0, which is alrite

    when going on to solve x and y, i end up with:

    x=-2
    x=2.5
    putting these into y=3x+11 i got:

    y=5
    y=18.5

    finally giving the intersections of (-2,5) and (2.5,18.5)

    however the answers given by the textbook from which the question was taken from, the intersections are (-1.5,6.5) and (2,17)

    im really confused and would be much obliged for any help given

    thank you
     
  2. jcsd
  3. Oct 23, 2004 #2

    arildno

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    Is 4*2.5=6?????
     
  4. Oct 23, 2004 #3
    its 4*-2.5=-6
     
  5. Oct 23, 2004 #4

    HallsofIvy

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    Remarkable. My calculator says that 4* -2.5= -10.

    4*(2- .5)= 6
     
  6. Oct 23, 2004 #5

    arildno

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    4*(-2.5)=-10
     
  7. Oct 23, 2004 #6
    omg!! i feel so goddamn stupid! :blushing:

    thnx guys. i dont think i should be doing as level maths if i cant do 4*-2.5!!

    thnx again.
     
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