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Math Help - Is my answers page completely broken? or am I?

  1. #1
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    Is my answers page completely broken? or am I?

    y=3x+11
    y=x^2+4x+5

    • 3x+11=x^2+4x+5
    • 11=x^2+x+5
    • 6=x^2+x
    • x^2+x-6=0
    • (x-3)(x+2)
    • So! I think x = 2  or -3

    so
    When x=2
    y=6+11
    y=17

    x=-3
    y=-9+11
    y=2<br />
    My answers page says the co-ords are (2,-3) as in x =2 and y = -3

    Putting x as -3 in y=x^2+4x+5 Gives y=9-12+5 = 2

    SO to me x = -3 and y = 2. But the answers page says other wise, who's right?
    I've already had 1 answer wrong in this book!
    Last edited by sxsniper; January 20th 2011 at 06:39 AM.
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  2. #2
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    3x + 11 = x^2  + x + 5\;\; \to \;\;x^2  - 2x - 6 = 0
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  3. #3
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    Sorry I wrote it down wrong, try again
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  4. #4
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    Quote Originally Posted by sxsniper View Post
    y=3x+11
    y=x^2+4x+5
    The way you solved above tired ME out!
    Try keeping it simpler (so your teacher will not give up!), like:

    x^2 + 4x + 5 = 3x + 11
    x^2 + 4x - 3x + 5 - 11 = 0
    x^2 + x - 6 = 0
    (x + 3)(x - 2) = 0
    x = -3 or x = 2

    Now, using y = 3x + 11 :
    when x = -3, y = 3(-3) + 11 = 2
    when x = 2, y = 3(2) + 11 = 17

    Now you and/or your book can rant and rave, but the (x,y) solutions are:
    (-3,2) and (2,17) ; over and out
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  5. #5
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    Thanks, I don't have a teacher, I'm learning for the fun of it.
    It tires me out too! But at least I can see exactly what I've done.

    This book sucks, I think someone just put random numbers in the answers page.
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  6. #6
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    Quote Originally Posted by sxsniper View Post
    y=3x+11
    y=x^2+4x+5

    • 3x+11=x^2+4x+5
    • 11=x^2+x+5
    • 6=x^2+x
    • x^2+x-6=0
    • (x-3)(x+2)
    • So! I think x = 2  or -3
    This is incorrect. "If ab= 0 then either a= 0 or b= 0". You have (x- 3)(x+ 2)= 0 so either x- 3= 0 or x+ 2= 0. Then x= 3 or x= -2, not "x= 2 or -3"

    so
    When x=2
    y=6+11
    y=17

    x=-3
    y=-9+11
    y=2<br />
    My answers page says the co-ords are (2,-3) as in x =2 and y = -3
    As I said before, x= -2 or x= 3. If x= -2, then y= 3(-2)+ 11= 5. If x= 3, y= 3(3)+ 11= 20. the correct solutions are (-2, 5) and (3, 20).

    Putting x as -3 in y=x^2+4x+5 Gives y=9-12+5 = 2

    SO to me x = -3 and y = 2. But the answers page says other wise, who's right?
    I've already had 1 answer wrong in this book!
    Did you check your answers by putting them back into the equations?
    Last edited by HallsofIvy; January 22nd 2011 at 04:44 AM.
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  7. #7
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    You've just wrecked every hope I had, I understood it until you posted that. It's the format mess the post is in that's throwing me off.


    So X could equal either 3 or -2. I actually wrote that down wrong and continued from my error (I even wrote it down wrong when typing this up!). I am prone to writing things down wrong ! And failing the maths due to negligence.

    After de-cyphering the format of your post it all makes sense.

    Very helpful.
    Cheers, that was pretty a pretty serious error.

    Edit: You can see I checked, you corrected it.
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  8. #8
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     x^2+x-6

    is  (x+3)(x-2)

    Since 3-2 = 1 (which is coefficient of x)

    That's all you did wrong....
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