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Homework Help: Grade 9/10 Algebra.

  1. Sep 9, 2009 #1
    (8y squared + 5y -7) - ( 9y squared + 3x -3)

    This is my friends, and i'm trying to hlep him on it.
    And the answer in the book is -y squared +8y -12
    and we can't figure out how to get it.
  2. jcsd
  3. Sep 9, 2009 #2


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    Well something is missing in the initial equation.

    (8y2 + 5y -7) - (9y2 + 3x -3) = 0 ?

    and one is solving for x?

    or (8y2 + 5y -7) - (9y2 + 3y -3) = ?

    in which case one simply groups the corresponding monomials, or powers of y.

    This looks like homework so I'll move it to the precalculus HW forum.
  4. Sep 9, 2009 #3
    I don't think that's what it's asking for. It's just simplifying it.
    I wrote what it says the answer is.
    But i got like -y squared -3x+5y-4
  5. Sep 9, 2009 #4
    If all you are supposed to do is simplify the expression, and that line is all that you are given about x and y, then the book is incorrect.
  6. Sep 9, 2009 #5
    okay, i thought the book was wrong but just thought i'd make sure.
    and there is no way 7 and 3 can make 12.
  7. Sep 9, 2009 #6
    One of three things could be happening:

    (1) There is a typo in the book (it happens) and the problem should have read


    (2) The person who wrote the solution erred (it happens - solution manual writers are rarely the original text authors).

    (3) There is somewhere an assumption that [itex]x = \frac{22}{3}-y[/itex].

    Regardless, the problem as stated and the given answer do not correspond.

  8. Sep 10, 2009 #7


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    [itex](8y^2+ 5y- 7)[/itex][itex]- (9y^2+ 3x- 3)[/itex][itex]= (8y^2- 9y^2)+ (5y- 3y)+ (-7- (-3))[/itex] is NOT [itex]-y^2+ 8y- 12[/itex].
  9. Sep 10, 2009 #8
    Especially since there is a 3x in there.

  10. Sep 10, 2009 #9
    If Jenninifer typed the way he/she should of at his/her first post in this topic, then the answer in the book is wrong!
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