Answer:
Step-by-step explanation:
Let z = x - y
The given expression translates into
(z + 7)(z - 7) which is going to give you the difference of squares.
z^2 - 49
Now you need to know what z^2 is
z = x -y
z^2 = x^2 - 2xy + y^2
So the answer becomes
x^2 - 2xy + y^2 - 49
