b Solve for t when the function is equal to the given value.
A
a 4 500 000 kilometers
B
b 40 seconds
Practice makes perfect
a The exercise gives us a function that describes the distance that light travels in t seconds.
d(t)=300 000t
In the above formula, d(t) represents the distance, in kilometers, and t represents the time, in seconds. Calculating the distance that light travels in 15 seconds is the same as evaluating d(t) for t=15. We can do this by substituting 15 for every instance of t in the function.
In 15 seconds, light travels 4 500 000 kilometers.
b In this case, we are given the distance, and need to calculate the time.
d(t)=300 000 t
Calculating the time it would take for light to travel 12 000 000 kilometers means that we will need to substitute this distance for d(t) in the function, and solve for t.
