(5x^3-3y^3)^2-(3x^3-5y^3)^2=[(5x^3-3y^3)+(3x^3-5y^3)][(5x^3-3y^3)-(3x^3-5y^3)]=(8x^3-8y^3)(2x^3+2y^3)=16(x^3-y^3)(x^3+y^3)=16(x-y)(x^2+xy+y^2)(x+y)(x^2-xy+y^2)