①(-x)^3·x·(-x)^4÷x^5
=-x^4*(-x)^4÷x^5
=x^8÷x^5
=x^3
②(x^3)^4+x^10·x^2+x·x^3·x^8
=x^12+x^12+x^12
=3x^12
③(16x^2y^3z+8x^3y^2z)÷8x^2y^2
=2yz+xz
④(2x+y)(x-y)-(x+2y)^2
=2x^2+xy-2xy-y^2-x^2-4y^2-4xy
=x^2-5xy-5y^2