Grade 9/10 Algebra.

[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.

[Astronuc]

(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. 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.

[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

[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.

[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.

[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

[HallsofIvy]

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

[Elucidus]

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

Especially since there is a 3x in there.

--Elucidus

[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!