唔該大家計幾條指數

1. (3a^2*b^-3)(5a^-4*b^7)

3a^2 b^7
=---- * -----
b^3 5a^4

3b^4
=-----------
5a^2


2.(2x^-2*y)^-4(x^6*y^-2)^-2

= (2x^8*y^-4) (x^-12*y^4)

2x^8 y^4
=---------- *-----------
y^4 x^12

2
=---------
x^4