To determine which function is nonlinear, let's analyze each of the given functions:
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y = (5/8)x: This is a linear function because it is in the form \(y = mx + b\), where \(m = 5/8\) and \(b = 0\).
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y = 8·2^(x − 9): This is an exponential function because it includes the variable \(x\) as an exponent. Thus, this function is nonlinear.
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y = 12x + 8: This is also a linear function in the form \(y = mx + b\), where \(m = 12\) and \(b = 8\).
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y = 5.2(7.1)^x: This is another exponential function (similar to the second function) because of the variable \(x\) being in the exponent.
From these analyses, the two nonlinear functions are y = 8·2^(x − 9) and y = 5.2(7.1)^x. However, since you are looking for a single nonlinear function, the first one listed as nonlinear is:
y = 8·2^(x − 9).
This is the function you would choose as nonlinear.