[(-2a^2b)/(3c)]^-2
=1/[(-2a^2b)/(3c)]^2
=[(3c)/[(-2a^2b)]^2
=9c^2/4a^4b^2问一下：第一步是怎么得出的？负指数幂=1/相反数幂，即当n>0时，m^（-n）=1/m^n