## niikofi12 2 years ago what duz it mean to say "(a+b) is composite"?

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1. kirbykirby

It just means it is not prime, meaning there is a divisor that is not just 1 and itself

2. kirbykirby

For example, 2, 3, 5, 7, 11 are prime but 4, 6, 15, 21 are composite (2*2=4, 2*3=6, 3*5=15, 7*3=21)

3. niikofi12

thanks! u r d best!

4. kirbykirby

:) np

5. niikofi12

one mor fn...if u hv X={1,2,3,...,10} n aRb( a relates b) such dat (a+b) is composite. wat r the elements of the relation?

6. niikofi12

is it (1,3),(1,5),(1,7),(1,8),...?

7. niikofi12

@kirbykirby?

8. kirbykirby

yes it would be any pair (a,b) such that adding both together "a+b" gives a composite number Although I'm not too sure if the sum can't be greater than 10. I never saw this "Rb" notation. Does it say anywhere that (a+b) belongs to X ?

9. niikofi12

i think so cuz it says "... and R a relation on X defined by aRb:a+b is composite"

10. niikofi12

cuz X is limited on d range 1-10

11. niikofi12

wat do u fnk?

12. kirbykirby

ok then I would think that the sum can't exceed 10 (but I am not 100% sure o_o)

13. niikofi12

me neither. thanks anyway

14. kirbykirby

but fairly certain. Otherwise I think you'd have too many pairs to list lol