Question 196763
(x+3y)/(x-3y)  -  (x-3y) /(x+3y)
.
{(x+3y)^2 - (x-3y)^2} / { x-3y)(x+3y) }
 .
{ {x^2 +6xy +9y^2}  - {x^2 -6xy +9y^2} ] / { (x-3y)(x+3y) }
.
12xy / { (x-3y)(x+3y) }
.
12xy / (x^2 -9y^2) 
.