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.
A)
Let and .
Also, let e be the unity of J.
Then, (since I is an ideal of R and e is also in I)
And so (since J is an ideal of I)
But
i.e
Hence, J is an ideal of R.
B) Consider and
Let R = , I and J =
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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