\(D=\left[x^2\left(x+y\right)+x^2\right]-\left[y^2\left(x+y\right)+y^2\right]+\left[2\left(x+y\right)+2\right]+1\)
\(D=\left[x^2\left(x+y+1\right)\right]-\left[y^2\left(x+y+1\right)\right]+\left[2\left(x+y+1\right)\right]+1\)
\(D=\left[0\right]+\left[0\right]+\left[0\right]+1=1\)
Đáp số : D=1