00:01
So in this question, i'm going to find the four second partial derivatives, and i'm going to evaluate each at the given point.
00:07
So here my function is f of xy equals x cubed plus 3xy cubed minus 9y.
00:14
So let's get my partial of f with respect to x.
00:19
And that should be 3x squared plus 3y cubed.
00:27
There's f sub xx.
00:28
So now let's get f sub xx.
00:34
That should just be 6x.
00:37
And if i evaluate this at the point 9 comma 3, 6 times 9 is 54.
00:45
Now let's get f sub xy.
00:49
So my f sub x y this time looks like 9 y squared.
00:55
I evaluate this at 9 .3.
00:58
I'm getting 9 times 3 squared, 9 times 3 squared.
01:03
It is 9 times 9 or 81...