Final answer:
The rate of change in the function f(x)=8x is 8, which represents the bicyclist's constant speed of 8 miles per hour in this situation.
Step-by-step explanation:
The rate of change in the given function f(x)=8x, which represents the distance in miles that a bicyclist is from home after riding for x hours, is 8. This rate of change is the coefficient of x in the linear function and represents the constant speed at which the bicyclist is traveling. Therefore, the bicyclist is riding at a speed of 8 miles per hour.
To visualize this, imagine a position versus time graph where the x-axis represents time in hours, and the y-axis represents position in miles. Given that the line starts with an initial value of d=0 at t=0, it crosses the x-axis at the origin, which is the initial position. As time increases, the line will rise steadily, reflecting the uniform rate at which the distance from home increases. The slope of this line, which is the rate of change, is the speed of the bicyclist, and it represents how many miles are covered per hour ridden.