\(a,=5x\left(x-1\right)+y\left(x-1\right)=\left(5x+y\right)\left(x-1\right)\\ b,=\left(x-y\right)^2-9=\left(x-y-3\right)\left(x-y+3\right)\)
a)5x2-5x+xy-y=(5x2-5x)+(xy-y)=5x(x-1)+y(x-1)=(x-1)(5x+y)
b)x2-2xy+y2-9=(x2-2xy+y2)-9=(x-y)2-32=(x-y-3)(x-y+3)