Answer to Question #107070 in Abstract Algebra for Garima Ahlawat

Question #107070
Give a non trivial element of the ring Z10 / <4bar> , with justification.
1
Expert's answer
2020-03-31T15:55:46-0400

The given ring is ,


"\\frac{\\Z_{10}}{<\\bar4>}=\\{ \\bar b +<\\bar4>:\\bar b\\in \\Z_{10} \\}=G(say)"


Where "<\\bar4>= \\{ \\bar0,\\bar2,\\bar4,\\bar6,\\bar8\\}" .

Then a element "x=\\bar b+<\\bar4>\\in G" is called non trivial if "x\\neq<\\bar4>" .

Again ,we known that "\\bar a+<\\bar4>=<\\bar4> \\iff \\bar a\\in <\\bar4>"

as a coset .

We can easily prove it ,

Suppose that "\\bar a+<\\bar4>=<\\bar4>"

Then ,"\\bar a+\\bar0 \\in \\bar a +<\\bar4> =<\\bar4>" .

Conversely ,assume that "\\bar a\\in <\\bar4>" .

Since ,"<\\bar4>" is a subgroup ,therefore by closer property

"\\bar a+\\bar y\\in <\\bar4> \\forall \\ \\bar y \\in <\\bar4> \\implies \\bar y +<\\bar4>\\subseteq<\\bar4>" .

Let "\\bar y\\in <\\bar4>." Since "\\bar a ,\\bar y \\in <\\bar 4>" therefore "\\bar y-\\bar a\\in<\\bar4>."

Thus , "\\bar y = \\bar0+\\bar y=(\\bar a -\\bar a)+\\bar y=\\bar a +(\\bar y-\\bar a)\\in \\bar a +<\\bar4 >"

Hence,"\\bar a +<\\bar 4>=<\\bar 4>" .

Since , "\\bar3 \\notin <\\bar4> \\implies \\bar3+<\\bar4>" is a non trivial element of G.



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