Question 971896
What subtracting?  You mention, "subtracting rational expressions", but you show partly using a word, division of rational expressions.  


Operator precedence gives higher priority to division than to subtraction.  Your ratio of rational expressions should be handled, or simplified, first.  Yes, you would invert the second rational expression and multiply it by the first rational expression.


You might also try to factorize any rational expressions afterwards, depending on what your problem's goals are.