\(-x-y^2+x^2-y=-\left(x+y\right)-\left(x-y\right)\left(x+y\right)=\left(x+y\right)\left(-1-x+y\right)\)
x-y2+x2-y
=(x-y)+(x2-y2)
=(x-y)+(x-y)(x+y)
=(x-y)(1+x+y)
\(-x-y^2+x^2-y=-\left(x+y\right)-\left(x-y\right)\left(x+y\right)=\left(x+y\right)\left(-1-x+y\right)\)
x-y2+x2-y
=(x-y)+(x2-y2)
=(x-y)+(x-y)(x+y)
=(x-y)(1+x+y)