① (a+b)(a^2-ab+b^2) =a^3-a^2b+ab^2+a^2b-ab^2+b^3 =a^3+b^3 ②（3xy)^2/xy+(x-y)^2-(x+y)(x-y) =3xy+x^2-2xy+y^2-x^2+y^2 =xy+2y^2 ③(a-b)^2+b(a-b) =(a-b)(a-b+b) =a(a-b) =a^2-ab ④(3x+2)(3x-2)-5x(x-1)-(2x-1)^2 =9x^2-4-5x^2+5x-4x^2+4x-1 =9x-5