a, = (xy-y^2) + (2x-2y) = y(x-y) + 2.(x-y) = (x-y).(y+2) 

b, = (x+y)^2 - 9 = (x+y-3).(x+y+3)

\(xy-y^2-2x-2y\)   

=(xy-y).(2x-2y)

=y(x-y).2(x-y)

=(x-y).(y-2)

camr ơn bạn nha

\(ab\left(x^2+y^2\right)-xy\left(a^2+b^2\right)\)

\(=abx^2+aby^2-a^2xy-b^2xy\)

\(=ax\left(bx-ay\right)+by\left(ay-bx\right)\)

\(=ax\left(bx-ay\right)-by\left(bx-ay\right)\)

\(\left(bx-ay\right)\left(ax-by\right)\)

hãy k nếu bạn thấy đây là câu tl đúng :)

Thanks 

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

\(=x\left(y-1\right)+y\left(y-1\right)-x^2\left(y^2-1\right)\)\(=\left(y-1\right)\left[x+y-x^2\left(y+1\right)\right]\)

\(=\left(y-1\right)\left(x+y-x^2y-x^2\right)\)\(=\left(y-1\right)\left[x\left(1-x\right)+y\left(1-x^2\right)\right]\)

\(=\left(y-1\right)\left(1-x\right)\left[x+y\left(1+x\right)\right]=\left(y-1\right)\left(1-x\right)\left(xy+x+y\right)\)

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

\(=x^2y^2+xy-x^2y+xy^2+xy+1-x+y+x^2y+x-x^2+xy-xy^2-y+xy-y^2\)

\(=x^2y^2+2xy-x^2-y^2+1\)

\(x^2-x-4y^2-2y\)

\(=x^2-4y^2-\left(x+2y\right)\)

\(=\left(x-2y\right)\left(x+2y\right)-\left(x+2y\right)\)

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