Typo in "Algebra Demystified"?

[maroonblazer]

Hi all,
For those who have this book, I'm working through the Chapter Review for Chapter 6 "Factoring".

Problem #11 is:
15/(45xy^2 + 30x + 15)

The answer I arrived at is:
1/(3xy^2 + 2x +1)

However the book states the correct answer to be:
1/(3x^2y + 2x +1)

This makes no sense to me. Further, my answer isn't even one of the other 3 options (the review is multiple choice).

Is this just a typo in the book? Or am I missing a critical step?

Thanks in advance!
mb

[stapel_eliz]

It looks like a typo to me.

[maroonblazer]

Maybe I should've made the subject "TypoS in 'Algebra Demystified'"...

Here's problem #18, Chp 6 Review (Factoring):

(7/(x^2)+3x-18) - (1/(x^2)+x-12)

My answer is (6x+22)/((x-6)(x+3)(x+4))

The book says the correct answer has the numerator as: 6x-22 (we have the same denominator).

I can't figure out how/why the 22 would be negative...?

Help?

[stapel_eliz]

What were your steps in working the exercise?

[maroonblazer]

I factored the denominator of the first fraction to get: (x+6)(x-3)

I factored the denominator of the second fraction to: (x+4)(x-3)

I multiplied the first fraction by (x+4)/(x+4) to get: 7(x+4)/(x+6)(x-3)(x+4)

I multiplied the second fraction by (x+6)/(x+6) to get: (x+6)/(x+6)(x-3)(x+4)

7(x+4) = 7x+28

Put it all together and you get (in the numerator): 7x+28-(x+6)

Distribute the "-" in "-(x+6)" gives: -x-6

Add -x to 7x gives 6x. add -6 to 28 give +22.

[stapel_eliz]

The denominators you show in your work (thank you!) differ from what you'd shown earlier in your final result. At a guess, whatever graduate student was assigned this exercise typoed a sign in the numerator, whereas you'd typoed signs in the denominators.

Typoes happen, but they should be much-more-thoroughly corrected in solutions for students at your level, especially in a book which is intended to help students!

[maroonblazer]

Argh, sorry about that. I shouldn't do math when I'm exhausted.

Really appreciate the help!