It is well known that an extension field is a linear space over basic field, when the extension field is a Galois extension, every Galois action can be seen a linear transformation.

• 我们可以认为扩张域就是基域上的线性空间,当这个域扩张是Galois扩张时,每个Galois作用可以看作上述线性空间的线性变换。