Answer to Question #133617 in Abstract Algebra for PRATHIBHA ROSE C S

Question #133617
Find the number of elements of order 9 in Z3 (product ) Z9
1
Expert's answer
2020-09-23T17:27:44-0400

We know that

The order of an element in a direct product of finite number of finite groups is the least common multiple of the order of components of the element. In symbols,

(g1,g2,.........,gn)=|(g_1,g_2,.........,g_n)|= lcm (g1,g2,..........,gn)(|g_1|,|g_2|,..........,|g_n|)

Therefore, We may count the number of elements (a,b)(a,b) in Z3Z9\Z_3 \bigoplus \Z_9 with the property that ,

9=(a,b)=9=|(a,b)|= lcm (a,b)(|a|,|b|) .

Clearly, this requires either a=1|a|=1 and b=9|b|=9 or a=3|a|=3 and b=9|b|=9 .

Case:1 a=1|a|=1 and b=9|b|=9

Here there are 1 choice for aa and 6 choices for bb ( namely 1,2,4,5,7 and 8).

This gives 1×6=61×6=6 element of order 9.

Case 2. a=3|a|=3 and b=9|b|=9

This time 2 choices for aa (namely, 1, and 2) and as before 6 choices for bb .

This gives 2×6=122×6=12 elements.

Therefore the total number of elements of order 9 is 6+12=18.


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Comments

Assignment Expert
24.09.20, 18:38

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PRATHIBHA ROSE C S
24.09.20, 06:34

Thank you so much assignment expert

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