计算:(3a+1)的2次方乘(3a-1)的2次方等于

问题描述:

计算:(3a+1)的2次方乘(3a-1)的2次方等于
A:9a的2次方-1
B:81a的4次方-1
C:81a的2次方-18a的2次方+1
D:81a的4次方+18a的2次方+1

含韵★Baby,
(3a+1)^2(3a-1)^2
=[(3a+1)(3a-1)]^2
=(9a^2-1)^2
=81a^4-18a^2+1
选C