Question 475010
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Hi
Per your reply: see highlighted, this type of operation is commonly done
to achieve common denominators when it is appropriate to do so.
Note: using parenthesis clarifys:
(6-w)/(w-9)  -  (9w-7)/(9-w)  |Note:  {{{highlight((9-w) = -(w-9))}}}
{{{(6-w)/(w-9)  -  (9w-7)/(-(w-9))}}}

{{{(6-w)/(w-9)  +  (9w-7)/(w-9)  = (8w-1)/(w-9)}}}