1. Sep 9, 2009

Jenninifer

(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. Sep 9, 2009

Astronuc

Staff Emeritus
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.

3. Sep 9, 2009

Jenninifer

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

4. Sep 9, 2009

slider142

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.

5. Sep 9, 2009

Jenninifer

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.

6. Sep 9, 2009

Elucidus

One of three things could be happening:

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

$$(8y^2+5y+7)-(9y^2-3y-5)$$.

(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 $x = \frac{22}{3}-y$.

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

--Elucidus

7. Sep 10, 2009

HallsofIvy

$(8y^2+ 5y- 7)$$- (9y^2+ 3x- 3)$$= (8y^2- 9y^2)+ (5y- 3y)+ (-7- (-3))$ is NOT $-y^2+ 8y- 12$.

8. Sep 10, 2009

Elucidus

Especially since there is a 3x in there.

--Elucidus

9. Sep 10, 2009

jhooper3581

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!