(a^2 - 1) / (-a - 1)
Answer key: 1 - a
This looks like another simple problem. But I tried AfterShock method of splitting the numerator and find nothing to cancel; I also tried Dan's suggestion of factoring, I don't think I see something to factor. This one seems harder, how to arrive at 1 - a solution?
(a^2 - 1)/(-a - 1) = (a^2)/(-a - 1) + (-1/(-a-1))
= (-a^2)/(a + 1) + 1/(a + 1)
In the above step, I just made it so that the denominator was positive and the numerator negative, and in the second both positive. Personal preference.
We can expand the first set of terms by long division:
(-a + 1) + -1/(a+1) + 1/(a+1) = (-a + 1)