Algebra - exponents - help please!! Fast!

Factual Questions
1

I have to leave in 1 hour to go take my Algebra midterm and there’s 1 thing that is really annoying me.

I have done this (and similar) problems many times and I’m wrong every time (according to mymathlab) and I just don’t understand why.

-28a^6b^-3c^9/-4a^-7b^-2c^-7

This is how I work it out:

-28/-4=7

a^6-(-7)=a^13

b^-3-(-2)=b^-1

c^9-(-7)=c^16

Final answer is:

7a^13c^16/b

mymathlab’s final answer is:

7a^13bc^16
I posted this on our class discussion board 2 days ago. One classmate said she got the same (wrong) answer I got and the professor hasn’t answered.

I can’t figure out why I’m wrong. I don’t generally have issues with exponents. Please someone explain this in layman’s terms for me? Within the next 45 minutes?

Thanks.

2

What you’ve written is correct, given the problem as you’ve stated it. What exactly are you typing into mymathlab?

3

As far as I can tell, you are correct.

4

Thanks guys. I’m typing it into mymathlab exactly the same (well, with real exponents, not with carots) and it keeps saying that the b belongs above the line.

Luckily the midterm is a paper and pencil test so I’m not relying on a computer to have the right answer.

5

You’re not using any parentheses as you type it in?

6

I was thinking the same thing about parentheses.
Some math parsers have some difficulties without parens in the right place.

7

No parentheses. As far as I can tell, there is no need for them. If I put them in and it wasn’t expecting them, I’d definitely get it wrong.

8

Without parentheses, I’d parse it completely differently. I’d think you were only dividing by -4, and still multiplying by a^-7b^-2c^-7. But that wouldn’t produce what you got; it would produce 7a^-1b^-5c^2.

9

When in doubt on a computer or calculator, put in parentheses. If you put them in in the right places, then it should never cause problems.

10

I got 100 on my midterm, thankfully. This one test was worth 50% of my final grade.

There were a couple problems dealing with exponents but this issue didn’t come up.

Thanks for the answers guys.

11

The only thing I can think of that might be the culprit would be either a display error or a reading error. I’m guessing mymathlab is trying to display:

7a[sup]13[/sup]b[sup]-1[/sup]c[sup]16[/sup]

…and somehow the [sup]-1[/sup] isn’t legible.

12

I’m not familiar with mymathlab–is there a possibility that it’s simply wrong?

(I do know that the odd-numbered answers in the back of the book aren’t infallible.)