2) (y+3) (y+1) = y^2 + y + 3y + 3 = y^2 + 4y + 3
3) (x+4) (y-4) = xy - 4x + 4y - 16
4) (x+2) (y-1) = xy - x + 2y - 2
5) (x+a) (y-a) = xy - ax + ay - a^2 = xy + (a-x)y - a^2 = xy + ay - xy - a^2 = ay - a^2
6) (a+x) (a-y) = ay - a^2 + ax - xy = ax + ay - xy - a^2
7) (-m-n) (m-n) = -m^2 + mn - nm + n^2 = -m^2 + n^2
8) (a-b) (-a-b) = -a^2 - ab + ab + b^2 = -a^2 - b^2
2) (y+3) (y+1) = y^2 + y + 3y + 3 = y^2 + 4y + 3
3) (x+4) (y-4) = xy - 4x + 4y - 16
4) (x+2) (y-1) = xy - x + 2y - 2
5) (x+a) (y-a) = xy - ax + ay - a^2 = xy + (a-x)y - a^2 = xy + ay - xy - a^2 = ay - a^2
6) (a+x) (a-y) = ay - a^2 + ax - xy = ax + ay - xy - a^2
7) (-m-n) (m-n) = -m^2 + mn - nm + n^2 = -m^2 + n^2
8) (a-b) (-a-b) = -a^2 - ab + ab + b^2 = -a^2 - b^2