00:01
So in this question, the temperature h in degrees celsius of a cup of coffee placed on the kitchen counter is given by h equals f of t, where t is in minutes since the coffee was put on the counter.
00:12
In part a, they say, is f prime of t positive or negative? you are correct that f prime of t is negative.
00:20
Why is that the case? the reason is because the temperature of the coffee is decreasing, so my rate of change should be negative this time.
00:30
Now, i agree that the units on f prime of 10 should be in degrees celsius per minute.
00:38
It is a rate of change, so it's units of h or units of f degrees celsius, divided by units of time, minutes.
00:47
Now, suppose that the absolute value of f prime of 10 is 1 .3, and the f of 10 is 52.
00:55
What does this mean? it means, indeed, that at 10 minutes after the coffee was put on the counter, its temperature is what? well, that's the value of the function.
01:10
So the value of the function is 52.
01:14
So 52 degrees celsius is the temperature of the coffee at 10 minutes.
01:22
And that temperature will indeed decrease...