Factoring question (56m^2-15m-56)

[Nakura Chambers]

I am working on this math problem and I was really proud of myself when I thought that I had found the answer without checking my notes or receiving any help. Unfortunately, it would seem that my elation was premature, as apparently I got the answer "wrong," even though I don't understand where I could have possibly made a mistake.

Can someone explain to me where I went wrong and why?

My work:


All of the writing on the page is mine.

[MerinPally]

I am working on this math problem and I was really proud of myself when I thought that I had found the answer without checking my notes or receiving any help. Unfortunately, it would seem that my elation was premature, as apparently I got the answer "wrong," even though I don't understand where I could have possibly made a mistake.

Can someone explain to me where I went wrong and why?

My work:
http://i61.tinypic.com/35d0x15.jpg

All of the writing on the page is mine.

Because you don't have -15m.

-7 * 7m = -49m.
8m * 8 = 64m.

You have +15m and not negative 15m. Swap the signs so that it's 7 * 7m and -8 * 8m and then you're golden.

[Nakura Chambers]

Signs are backwards!

Oh my, you are correct sir. I had been considering that as a possibility, but didn't want to risk being wrong and permanently getting the question incorrect (we only have three tries). Thank you!

[Independent voter]

wolfram alpha says a bunch of stuff that I don't understand and (8m + 7) (7m-8)

and it shows all the steps

[Elhana]

Oh my, you are correct sir. I had been considering that as a possibility, but didn't want to risk being wrong and permanently getting the question incorrect (we only have three tries).

It is very easy to check yourself - just multiply brackets again and see if you get stuff at the beginning.