00:01
So two cars are approaching an intersection on roads that are perpendicular.
00:06
Car a is north.
00:08
So car a is north and traveling south.
00:13
So i'm going to let this be a y distance.
00:18
Car b is east and traveling west.
00:23
I'm going to let that be an x distance.
00:27
And i want to know how fast the distance between them is changing.
00:31
So i really really have a right triangle.
00:35
Now, car a, or my rate, my d, y, dt is going to be negative 40 miles per hour.
00:46
Car b, i have dx, dt, and that is negative 50 miles per hour.
00:54
And i want to know how fast the distance between them is changing, so it's d, c, dt that i want.
01:02
So i'm going to to relate these variables.
01:05
I know that y squared plus x squared equals c squared.
01:11
Take the derivative...