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