\(a,=x\left(y-3\right)+y\left(y-3\right)=\left(x+y\right)\left(y-3\right)\\ b,=\left(x+2\right)^2-16y^2=\left(x+4y+2\right)\left(x-4y+2\right)\)
\(a,xy-3x+y^2-3y=\left(xy-3x\right)+\left(y^2-3y\right)=x\left(y-3\right)+y\left(y-3\right)=\left(x+y\right)\left(y-3\right)\\ b,x^2-16y^2+4x+4=\left(x^2+4x+4\right)-16y^2=\left(x+2\right)^2-\left(4y\right)^2=\left(x-4y+2\right)\left(x+4y+2\right)\)