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January 19th, 2012, 09:36 PM  #1 
Newbie Joined: Jun 2011 Posts: 8 Thanks: 0  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. 
January 19th, 2012, 09:43 PM  #2 
Senior Member Joined: Jul 2010 From: St. Augustine, FL., U.S.A.'s oldest city Posts: 12,155 Thanks: 462 Math Focus: Calculus/ODEs  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. 
January 19th, 2012, 09:58 PM  #3 
Newbie Joined: Jun 2011 Posts: 8 Thanks: 0  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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