what is the numerical coefficient of the a^8b^2 term in the expansion of (1/3a^2-3b)^6?
a^12/729 - (2 a^10 b)/27 + (5 a^8 b^2)/3 - 20 a^6 b^3 + 135 a^4 b^4 - 486 a^2 b^5 + 729 b^6
