Question 985281
Make x the subject of the formula:
(a+x)/(a-x) = (b-y)/(b+y)
<pre>
{{{(a+x)/(a-x) = (b-y)/(b+y)}}}

{{{(a+x)(b+y) = (b-y)(a-x)}}}

We will keep alphabetical order when multiplying 
two letters.

{{{ab+ay+bx+xy = ab-bx-ay+xy}}}

Subtract ab and xy from both sides:

{{{ay+bx = -bx-ay}}}

{{{2bx=-2ay}}}

{{{x=(-2ay)/(2b)}}}

{{{x=-ay/b}}}

Edwin</pre>