Raphael is traveling in a straight line at a constant speed from point a to point b. his distance from point b in miles is -20t+ 45, where t is number of hours he has been traveling. what is his speed in miles per hour?

Speed  = 20 mi/h

Explanation:

There are two points A and B

Distance between both the points are define with function -20t + 45 miles

where t represent the number of hours of travelling.

Now firstly we find the initial position. At starting time is 0, so we put t=0 in given function of t.

At t=0;

d₀ = -20(0) + 45 = 0 + 45 = 45 miles

Now we find the distance travell after starting first hour.

Than we put t = 1 in the given function

At t = 1;

d₁ = -20(1) + 45 = -20 + 45 = 25 miles

Difference between d₁ & d₀ is

45 - 25 = 20 miles

We see that in one hour, total distace is covered 20 miles

Now we use time, speed, distance relation

Speed = distance/time

Speed=

Speed = 20 miles/hour

That's the final answer.

I hope it will help you.

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