计算：
（-x/y^2)^4
(-4x^2y/3w)^3
(-6x^3y^4)除(-2xy)^3
(5x^4y^2-x^2y^4+3x^2y^2)除(-4x^2y)^2
(-x^3/2y)^2除(-a^2/b)^3*(b/2)^2