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January 19th, 2012, 09:36 PM   #1
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What am I doing wrong in this basic equation? Or am I wrong?

Here's a function: f(x) = 3x^2 - 2x - 9

I'm asked to determine the formula if x = (x - 5)

So I go ahead

3(x - 5)^2 - 2(x - 5) - 9
3(x^2 + 25) - 2x + 10 - 9
3x^2 + 75 - 2x + 10 - 9
3x^2 - 2x + 75 + 10 - 9

Final Answer:
3x^2 - 2x + 76

Except in the back of the book it says my answer should be this:

3x^2 - 32x + 76

Where the heck did that 32x come from? It seems impossible, but I know my answer has to be wrong because if I assign a value for the (x - 5), the one with a 32x appears to be the correct equation.
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January 19th, 2012, 09:43 PM   #2
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Re: What am I doing wrong in this basic equation? Or am I wr

Where you went wrong is saying:



when actually

(recall )

Try it again, and you will get the result your book has.
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January 19th, 2012, 09:58 PM   #3
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Re: What am I doing wrong in this basic equation? Or am I wr

Blah, thanks, I don't know why I missed that, we just did factoring of polynomials, should have gotten that lol.
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