(y - x)^2 = (-1)^2(x - y)^2 = (x - y)^2
Since squares are always positive, both are equal.
We write it as (x - y)^2 just to match the numerator, which is x - y. That way, we can simplify easily:
\frac{x - y}{(x - y)^2} = \frac{1}{x - y}
Which is exactly Quantity B.
We can do this because,
\frac{x - y}{(x - y)^2} = \frac{x-y}{(y-x)^2}
Example:
Let x = 4, y = 1
Quantity A:
\frac{4 - 1}{4^2 - 2(4)(1) + 1^2} = \frac{3}{16 - 8 + 1} = \frac{3}{9} = \frac{1}{3}
Quantity B:
\frac{1}{4 - 1} = \frac{1}{3}
You can do it the other way x = 1, y = 4. You will get the same result A=B
