Notice that you have denominators
 and . These are
called "reversed differences".

This is how we treat this: Take the
one which is not in descending order


write it in descending order:



factor out , which changes
both signs:



or just 

Now substitute that for:



Cancel the negative sign on the
bottom of the second fraction with
the minus sign in front of the
second fraction,making it a plus
in front of the second fraction:



Now the denominators are the same,
so all we need do is combine the
two numerators over their common
denominator:



or



Edwin