I am pretty sure this is an exercise in Atiyah-McDonald.
EDIT I just looked, and Exercises 2-5 in the first chapter have very similar statements, but not exactly the statement you are looking for...
I am pretty sure this is an exercise in Atiyah-McDonald.
EDIT I just looked, and Exercises 2-5 in the first chapter have very similar statements, but not exactly the statement you are looking for...