先化简,再求值:[5a^4*a^2-(3a^6)^2/(a^2)^3]/(-2a^2)^2,其中a=-5
问题描述：
先化简,再求值:[5a^4*a^2-(3a^6)^2/(a^2)^3]/(-2a^2)^2,其中a=-5
答
[5a^4*a^2-(3a^6)^2/(a^2)^3]/(-2a^2)^2
=(5a^6-9a^12/a^6)/(4a^4)
=(5a^6-9a^6)/(4a^4)
=-4a^6/(4a^4)
=-a^2