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Why This Equation Equals -1

  1. Feb 18, 2008 #1
    This is not a very difficult question, by any means, and I see that the answer does equal -1, but I do not see the mathematical steps that go on to prove that (y-2)/(2-y)=-1 .. Can someone show me the steps that go through that? Thanks in advance.
     
  2. jcsd
  3. Feb 18, 2008 #2
    Dude...

    1) (y-2)/(2-y)=-1
    2) (y-2)=-1(-y+2)
    3) (y-2)=(y-2)

    Wait a bit and I'll post the same in TeX.
     
  4. Feb 18, 2008 #3
    Better way.

    [tex]\frac{y-2}{2-y}=\frac{(y-2)(y+2)}{(2-y)(2+y)}=\frac{y^2-4}{4-y^2}=-1[/tex]
     
  5. Feb 18, 2008 #4
    lol, ok sorry. That was posted slightly incorrectly the first time. Basically, the textbook says "simplify: (y-2)/(2-y) " and the back of the book gives the final answer to be -1, so I can't do the left side right side stuff
     
  6. Feb 18, 2008 #5
    ahh, yes, I see your second post now . That does seem to be better. Thanks
     
  7. Feb 18, 2008 #6
    so basically what I do in your second post is I multiply the bottom and top by the conjugate of the denominator?
     
  8. Feb 18, 2008 #7
    Yes. (I had to look up what's a conjugate to answer your question.:shy:)

    In the future, could you please post your homework/assignment questions in the homework forum?


    This forum is more about theoretical discussions.
     
  9. Feb 18, 2008 #8
    Wow, I'm stupid...

    [tex]\frac{y-2}{2-y}=\frac{-1(2-y)}{2-y} =-1[/tex]

    This is what you get for not doing any maths for almost a year.
     
  10. Feb 18, 2008 #9
    OH! Jeeeze. I see, lol, Thanks. and, yes. Normally I post in the math homework forums but I think I just clicked on the wrong link and got here. I didn't notice that, sorry.
     
  11. Feb 18, 2008 #10

    JasonRox

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    I thought it was about general math.
     
  12. Feb 18, 2008 #11

    Hurkyl

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    (y-2)/(2-y) = -1 is an equation

    (y-2)/(2-y) is not an equation; it's an expression.
     
  13. Feb 18, 2008 #12

    Tom Mattson

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    It's -1 for all real numbers y not equal to 2. :wink:
     
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