Question #203323

Can there be a homomorphism from Z8 ⊕Z2 onto Z4⊕Z4 ? Give reasons for your

answer.


1
Expert's answer
2021-06-15T18:06:56-0400

Let us prove that there is no homomorphism from Z8Z2\Z_8 \otimes\Z_2 onto Z4×Z4\Z_4\times\Z_4 using method of contradiction. Assume that φ:Z8Z2Z4Z4\varphi:\Z_8 \otimes\Z_2 \to \Z_4 \otimes\Z_4 is a surjective homomorphism. Since Z8Z2=16=Z4Z4,|\Z_8 \otimes\Z_2|=16=|\Z_4 \otimes\Z_4 |, we conclude that the surjection φ\varphi is a bijection, and hence φ:Z8Z2Z4Z4\varphi:\Z_8 \otimes\Z_2 \to \Z_4 \otimes\Z_4 is an isomomorhism. Taking into account that isomorphisms preserve orders of elements and Z8Z2\Z_8 \otimes\Z_2 contains the element (1,0)(1,0) of order 8, but all elements of Z4Z4\Z_4 \otimes\Z_4 have order less or equal to 4, we conclude that our assumption is not true. Consequently, there is no homomorphism from Z8Z2\Z_8 \otimes\Z_2 onto Z4×Z4.\Z_4\times\Z_4.

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