Solve the following pair of linear equations:
$(a-b)x + (a+b)y = a^2 - 2ab - b^2$
$(a+b)(x+y) = a^2 + b^2$

Given equations are:
$(a-b)x + (a+b)y = a^2 - 2ab - b^2 \dots(1)$
$(a+b)(x+y) = a^2 + b^2 \dots(2)$
Expanding equation $(2)$:
$(a+b)x + (a+b)y = a^2 + b^2 \dots(3)$
Subtracting equation $(3)$ from $(1)$:
$[(a-b)x + (a+b)y] - [(a+b)x + (a+b)y] = (a^2 - 2ab - b^2) - (a^2 + b^2)$
$(a-b-a-b)x = -2ab - 2b^2$
$-2bx = -2b(a+b)$
$x = a+b$
Substituting $x = a+b$ into equation $(1)$:
$(a-b)(a+b) + (a+b)y = a^2 - 2ab - b^2$
$a^2 - b^2 + (a+b)y = a^2 - 2ab - b^2$
$(a+b)y = -2ab$
$y = \frac{-2ab}{a+b}$