A function is proportional if it can be expressed in the form \( y = kx \), where \( k \) is a constant. This means that the function passes through the origin (0,0) and maintains a constant ratio between \( y \) and \( x \).
Let's evaluate the given options:
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\( y = x + 12 \): This is not proportional because it does not pass through the origin; at \( x = 0 \), \( y = 12 \).
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\( y = x + \frac{1}{2} \): This is not proportional for the same reason; at \( x = 0 \), \( y = \frac{1}{2} \).
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\( y = 12x \): This is proportional because it can be written in the form \( y = kx \) with \( k = 12 \) and passes through the origin.
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\( y = \frac{1}{2} x \): This is also proportional in the form \( y = kx \) where \( k = \frac{1}{2} \) and also passes through the origin.
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\( y = x^2 \): This is not proportional because it does not pass through the origin in a linear fashion; at \( x = 0 \), \( y = 0 \) but it does not maintain a constant ratio.
Based on this analysis, the functions that are proportional are:
- \( y = 12x \)
- \( y = \frac{1}{2} x \)
So, the answer is \( y = 12x \) and \( y = \frac{1}{2} x \).