We first factor the numerator (top) then cancel.

`(x^2-y^2)/(y-x)` `=((x+y)(x-y))/(-(x-y))` `=(x+y)/-1` `=-x-y`

On the first line of the solution, I am changing the order of the (y − x) into (x − y) by placing a minus in front.

This is because

−(x − y)

= −x − (−y)

= −x + y

= y − x