00:01
This is a question about second order partial derivatives.
00:06
The question asks us to prove that this function, capital f, satisfies laplace's equation given here.
00:16
The derivative fxx plus the derivative fyy is zero.
00:25
So this should be quite simple.
00:28
We have to find these derivatives and then verify that their sum is zero.
00:33
To find the second order derivatives, we first find that.
00:36
The first order derivatives.
00:40
The derivative of this function with respect to x, we can find using chain rule because we have a function of x inside another function.
00:51
Now the outside function, arc tan of this quantity, which i'll call theta for now, is the derivative of arc tan theta with respect to theta, 1 over 1 plus theta squared, multiplied by the derivative of theta with respect to x and in that case if y is a constant and differentiate the x function.
01:36
Now instead of theta i'll write what the actually is and simplify a bit.
01:48
So, well right now we have a function or fractions within our fraction, so let's just multiply by x squared to get rid of that.
02:03
We multiply the top and bottom by x squared and we get this.
02:07
Now let's find the derivative with respect to x.
02:16
So, sorry, with respect to y...