求解答

在一公众号看到一题：If A sequence of operations{A1,A2,...An} is defined as follow A1(x)=x,A2(x)=2x2,...An(x)=nxn. if A2 is performed on x,and then A4 is performed on the result,what is the final result? (A)4x2 (B)8x2 (C)64x4 (D)64x8 (D)4x8
给出的答案过程：解题过程如下：
自变量发生改变后，函数就是An(2x2)=n(2x2)n,当n等与4时，A4(2x2)=4×(2x2)4=4×24×(x2)4=64x8

实在没看明白这个推算过程，求讲解。