Let R be the relation on the set A = {1, 2, 3, 4, 5, 6, 7} defined by the rule
( , ) a b R
if the integer product of (ab)
is divisible by 4. List the elements of R and its inverse?

So the first thing we do is to multiply the top equation by 3. the reason i want to do this is i notice there will be a 6y on both equations and can possibly add/subtract them. so we get 6y = -3x + 27. adding that and the second equation we get 6x = 27-15 which is 12. divide by 6 and we get 2. ∴ x = 2. substituting 2 into the first equation we get 2y = -2 + 9 which is 7. divide by 2 and we get 7/2. ∴ y = 7/2, x = 2.

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