Division of polynomials: answers not matching  TOPIC_SOLVED

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Division of polynomials: answers not matching

Postby myself5 on Thu Jan 22, 2009 5:09 pm

On Elementary Algebra page 243 problem 72, it says to divide 9x^2 – 9x – 28 by 3x+4. The answer they gave was 3x-7 with no remainder. My answer was 3x+ 21 with a remainder of 84 - 112. This is what I did:


Code: Select all
        3x + 21
     -------------
3x+4) 9x^2 – 9x – 28
     -9x^2 – 12x
     -------------
           - 21x – 28
           - 63x + 84
           -------------
              84 – 112



This is at least the third time I have had this problem in the last page and a half. Can anyone see where I went wrong?
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Postby stapel_eliz on Thu Jan 22, 2009 5:14 pm

myself5 wrote:...divide 9x^2 – 9x – 28 by 3x+4.

I'm not sure what you're doing in your second multiplication and subtraction...? :confused:

You did the first multiplication and subtraction, and ended up with -21x - 28 as your new dividend. Why did you multiply the 3x by -21 instead of by -7...? :oops:

Eliz.
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Re:

Postby myself5 on Fri Jan 23, 2009 3:21 pm

stapel_eliz wrote:You did the first multiplication and subtraction, and ended up with -21x - 28 as your new dividend. Why did you multiply the 3x by -21 instead of by -7...? :oops:


Yeah, it appears I was using the wrong number. I think I have it figured out now. Thanks so much for your help!
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