Let A = {1, 2, 3, ..., 14}. Define a relation R from A to A by R = {(x, y) : 3x - y = 0, where x, y ∈ A}. What is the domain of R?

Model Answer & Options

Source: Extra Practice

{1, 2, 3, 4}

{3, 6, 9, 12}

{1, 2, 3, 4, 5}

{1, 2, 3, ..., 14}

Explanation

The relation is defined by y = 3x. Since y must belong to set A (y ≤ 14), the possible values for x are: if x=1, y=3; if x=2, y=6; if x=3, y=9; if x=4, y=12. If x=5, y=15, which is not in A. The domain is the set of all first elements of the ordered pairs in R, which is {1, 2, 3, 4}. {3, 6, 9, 12} is the range, not the domain. {1, 2, 3, 4, 5} is incorrect because 5 has no image in A.

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