a, x3y - 9xy = xy(x2 - 9) = xy(x-3)(x+3)
b, x3 +y3 +2x2 -2xy+2y2 = (x^3 + y^3 ) + (2x^2 -2xy+2y^2 )
= (x+y)(x^2-xy+y^2)+2(x^2-xy+y^2)
=(x^2+xy+y^2)(x+y+2)
c, 5x^2 -5xy-9x+9y= 5x(x-y)-9(x-y)=(x-y)(5x-9)
d, m^3 +4m^2 +3m = m( m^2 +4m+3)=m(m^2+m+3m+3)=m(m+1)(m+3)