(a-1/9b^2)(3a+1/3b^2)(3a^2+1/27b^4)
=9(a-1/9b^2)(a+1/9b^2)(a^2+1/81b^4)
=9(a^2-1/81b^4)(a^2+1/81b^4)
=9(a^4-1/6561b^8)
=9 a^4-1/729b^8
如果本题有什么不明白可以追问,
(a-1/9b^2)(3a+1/3b^2)(3a^2+1/27b^4)
=9(a-1/9b^2)(a+1/9b^2)(a^2+1/81b^4)
=9(a^2-1/81b^4)(a^2+1/81b^4)
=9(a^4-1/6561b^8)
=9 a^4-1/729b^8
如果本题有什么不明白可以追问,