A proportional relationship can be identified through the general form of the equation \(y = kx\), where \(k\) is a constant. This means that the relationship passes through the origin (0,0) and does not have a constant added or subtracted.
Let's analyze each equation:
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y = x + 3: This is not proportional because of the +3; it does not pass through the origin.
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y = 3x + 1: This is not proportional because of the +1; it does not pass through the origin.
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y = 13x: This is proportional because it fits the form \(y = kx\) (with \(k = 13\)), and it passes through the origin.
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y = \frac{1}{3}x: This is also proportional because it fits the form \(y = kx\) (with \(k = \frac{1}{3}\)), and it passes through the origin.
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y = x^3 - 3: This is not proportional due to the -3 and the cubic term; it does not pass through the origin and is not in the required linear form.
Thus, the equations that represent a proportional relationship are:
- y = 13x
- y = \frac{1}{3}x