参考答案：

=cos[f(x²)]f’(x²)·2x=2xf’(x²)cos[f(x²)]，=2f’(x²)cos[f(x²)]+4x²f"(x²)cos[f(x²)]-4x²[f’(x²)]²sin[f(x²)]．

解析：[考点提示] 复合函数的二阶导数．