The poster made clever use of an arithmetical fact; no multiplication was necessary.
If you do 5 - 3, you get +2.
If you do 3 - 5, you get -2.
If you "reverse" a subtraction, you get an extra "minus" sign out front. The poster reversed the one subtraction in the denominator (to make the one factor "match" the others) and put the "minus" in front of the entire fraction (rather than leaving it in the denominator or putting it in front only of the numerator; either of these would be "correct", though).
Have fun!