00:01
We're given our function f, which is x squared plus y squared, and it's equal to 4.
00:05
So this is a level curve of the function f.
00:09
So we're asked to find the gradient of f at the given point, as well as write the equation for the tangents line.
00:17
Well, let us calculate the gradient first.
00:22
The gradient of f at the point root 2, root 2, that is going to be the partial derivative of f with respect to x.
00:32
Evaluated at the point and the partial derivative of y evaluated at the point.
00:46
So that is going to be equal to 2x and that'll be 2y.
01:01
So this is going to be 2 root 2 i plus 2 root 2 j.
01:11
The tangent line to the level curve at the point root 2 comma root 2 is given by the equation.
01:19
Partial f partial x at the point times x minus root 2 plus partial f partial y evaluated at the point times y minus y not which is root 2 equal into 0 and we know that this is 2 root 2 so you can plug it in 2 root 2 times x minus root 2 plus d .f, d, y is also 2 root 2.
02:04
So i'll plug it in.
02:09
Okay, so then this tells us 2 root 2x minus 4 plus 2 root 2y minus 4 is equal to 0...