Problem 3
This is not an exponential function. If you were to graph this out, you would see a parabola forming. Or at the very least, a parabolic-like curve forms. An exponential curve only increases or only decreases for the entire domain. However, in this case, we have an increasing portion, and then it decreases.
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Problem 4
This is an exponential function. Each time x increases by 1, y is multiplied by 4. The equation that models these points is y = 4^x. Note how the function is strictly increasing and there are no decreasing portions mixed in.