00:01
Okay, so for this question, we're given that a car is traveling north at 60 miles per hour, and a truck is traveling east at 45 miles per hour, and they both leave from the intersection at the exact same time.
00:12
So we're asked, what is the rate of change of the distance between them at two hours? so we know what are, we'll call this, before i get ahead of myself, we'll call this our y and this are x so we're asked what is d z d t so it's in correspondence to our z we have our d y d t which is 60 miles per hour we have our d x d t which is 45 miles per hour and so first things first this is a right triangle which means we're going to be using our pythagorean theorem x squared plus y squared is equal to z squared at some point in time.
01:10
So first things first, we do need to note the distance of x and the distance of y at two hours.
01:19
So if they're going, if y is going 60 miles per in one hour, in two hours, it will have driven 120 miles.
01:31
And so i just did 60 times 2 to get how much i'm going.
01:35
So if i'm driving 45 miles in one hour, then in two hours i will have driven 90 miles.
01:42
So now what is my length z at this time? so i want to know what z is because when i differentiate this equation right here, i need to differentiate all of them with respect to time because none of them are staying constant.
01:58
All of them are changing as we are going on with time.
02:02
So, in order to find my z, i need to take my 120 square that plus my 90 square that, square root, is equal to z...