Let be a commutative ring with unity.

If are distinct maximal ideals of , then

(1) .

(2) .

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- Mar 15th 2010, 09:28 PMKaKacomaximal(coprime)
Let be a commutative ring with unity.

If are distinct maximal ideals of , then

(1) .

(2) . - Mar 15th 2010, 11:45 PMaliceinwonderland
For (1), the sum of ideals is again an ideal (link). Thus, M+N is an ideal containing M. By hypthesis, M+N should properly contain an maximal ideal M. Thus M+N=A.

For (2), every proper ideal in A is contained in a maximal ideal in A and note that A contains the unity (link).

Assume is a proper ideal in A. Then, should be contained in a maximal ideal. It follows that should be contained in either M or N (check their intersection). Contradiction !

Thus, is an ideal in A which is not a proper ideal in A. We conclude that .