algebra

if f(x) = x^2 - 2x, find f(x+2) - f(2) / 2

the answer is: x+2

but l got: x^2 - 2x - 8 = 0

which is x = 4 or x = -2

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asked by dave
  1. =[(x+2)^2 - 2(x+2)] - [(2)^2 - 2(2)]/2
    =x^2+4x+4 - 2x-4 - (4-4)/2
    =x^2+2x - 0
    =x(x+2)
    = 0 or -2

    I have the x+2 part of your "correct answer", but I also got the "x" in there. That's the answer I came up with, if you don't understand how I arrive my answer, let me know.

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    posted by Jake1214
  2. wait, i mistyped. it should be:

    if f(x) = x^2 - 2x, find f(x+2) - f(2) / x

    divided by x, not 2.

    sorry...

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    posted by dave
  3. Hmm... that should be the same answer because f(2) = 0 and 0 divide by any number is 0 and "x" cannot be zero.

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    posted by Jake1214
  4. well i redid it and i got this:

    = x^2 + 4x + 4 - 2x - 4 - 2^2 - 4 / 2
    = x^2 + 2x / x

    divide the x and i get "x+2"

    is it correct??

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    posted by dave
  5. Where is the /x comes from on your x^2+2x/x... you were /2 up there on the above step... and even if the problem is f(2)/x... your f(2) = 0, that mean you get 0/x which equals 0, thus leaving you only x^2+2x on the left side, which equals x(x+2).

    Basically, I disagree with what you did up there because you can't just go from:

    x^2 + 2x - 0/x to (x^2 + 2x)/x

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    posted by Jake1214

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