Question #203329

Let R be a ring, I an ideal of R, J an ideal of I. Show that if J has a unity, then J is

an ideal of R. Also give an example to show that if J does not satisfy this condition

it need not be an ideal of R.


1
Expert's answer
2021-06-18T04:43:58-0400

A)

Let jJj \in J and rRr\in R.

Also, let e be the unity of J.

Then, reIre \in I (since I is an ideal of R and e is also in I)

And so (re)jJ(re)j \in J (since J is an ideal of I)

But (re)j=rj(re)j = rj

i.e rjJrj \in J

Hence, J is an ideal of R.

B) Consider Z4\mathbb{Z_4} and {0,2}\{0,2\}

Let R = Z4\mathbb{Z_4} , I =Z4= \mathbb{Z_4} and J = {0,2}\{0,2\}

We see from this example that the condition above will not be satisfied because, J has defined here is only a sub ring and not an ideal.




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