Chapter 4 - Exponential Functions - 4.3 Graphs of Exponential Functions - Exercises and Problems for Section 4.3 - Exercises and Problems - Page 163: 38

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As $a$ increases, the $y$-intercept of the curve rises, and the point of intersection shifts down and to the left and $y_0$ decreases. If $a$ becomes larger than $b$, the point of intersection shifts to the left side of the $y$-axis, and the value of $y_0$ continues to decrease but will not become 0.