00:01
This question gives us a scalar value function and wants us to find the gradient field of this function.
00:06
So what is the function? it's fee of x, comma, y, comma, z is equal to the natural log of 1 plus x squared plus y squared plus z squared.
00:16
The gradient field of fee is going to be equal to fee sub x, fee sub y, v sub z.
00:23
This notation, fee sub x, this is going to mean the partial derivative of fee with respect to x, just like fi sub y would mean partial derivative of f with respect to y.
00:33
This is just a shorthand notation for it.
00:36
F sub x.
00:38
So here we're going to have to use the chain rule.
00:40
We are in fact, well, for all three.
00:42
So for natural log, the derivative is one over the inside, which is one plus x squared plus y squared plus z squared.
00:48
Then we multiply it by the derivative of the inside.
00:51
Taking it term by term, derivative of the one is zero.
00:55
Derivative of the x squared is 2x by the power rule, and then derivative of the y squared plus z squared will be zero since we treat them as constants.
01:02
So it's just times 2x...