Answer
$(\mathrm{a})$
Work Step by Step
(a)
we can factor out -1 from the denominator,
$\displaystyle \frac{a-b}{b-a}=\frac{(a-b)}{-(a-b)}=$ ... cancel $(a-b)\quad=-1$
(b) cancels to 1
(c) and (d) have no common factors... cannot be simplified.
