M + N = \(x^2-2xy+y^2\)+\(y^2+2xy+x^2+1\)
= \(\left(x^2+x^2\right)+\left(-2xy+2xy\right)+\left(y^2+y^2\right)+1\)
= \(2x^2+2y^2+1\)
M - N = \(x^2-2xy+y^2-y^2+2xy+1\)
= \(\left(x^2+x^2\right)+\left(-2xy+2xy\right)+\left(y^2-y^2\right)+1\)
= \(2x^2+1\)