[代數] 幾題期中考的問題..

[paggei (XD)]

(1)  Prove that  a group that has only a finite number of subgroups
     must be finite.

(2) 舉一個無窮乘法循環群的例子

(3) G is group, H is a subgroup of G
    Prove that the number of all distinct right cosets of H in G is equal to
    the number of all distinct left cosets of H in C

即使考完了還是不會(炸)

想請問這幾題如何做呢@@

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