I am self studying Fields and Galois Theory from Algebra by Hungerford and I am unable to think about how to prove (iii) of lemma 2.6 given on Page 246 of the book.
Adding it's image->
Defination that could be useful -> H' is fixed field.
I tried firstly by simply using the definition and then assuming some x belongs to L and then trying to prove x belongs to L" .
But I am not able to successfully use these.