(1) x^4-x^3y
=x^3(x-y)
(2)2ab+6b
=2b(a+3)
(3)5x^2y+10xy^2-15xy
=5xy(x+2y-3)
(4)3x(m-n)+2(m-n)
=(m-n)(3x+2)
(5)3(x-3)^2-6(3-x)
=3(x-3)[(x-3)+2]
=3(x-3)(x-1)
(6)y^2(2x+1)+y(2x+1)^2
=y(2x+1)(y+2x+1)
(7)a^2b(a-b)+3ab(a-b)
=ab(a-b)(a+3)