I do not understand how you determine if a set is closed or open under a given operation.

Question

amistre64 · Answer

ever color in a coloring book?

anonymous · Answer

OK how do I determine if a set of natural numbers is closed or open with addition.

amistre64 · Answer

the rules are that you must stay in between the lines ...  same thing for an operation on a set;  in order to be closed, the solution has to be an element within the set

amistre64 · Answer

ah ... let a,b be elements of the natural numbers;

if the solution to a+b is NOT a natural number, for ANY a,b combinations, then the set is OPEN

if the solution to a+b IS a natural number, for ALL a,b combinations, then the set is CLOSED

anonymous · Answer

thank you

amistre64 · Answer

i cant really think of a good way to try to prove that 2 natural numbers sum to a natural number tho ... maybe by contradication?

anonymous · Answer

what about if you are subtracting

amistre64 · Answer

can you find 2 natural numbers that when subtracted is NOT a natural number?

amistre64 · Answer

is: 2 - 3 in the set of N ?